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CD-ROM Technical Summary
From Plastic Pits to "Fantasia"
Andy Poggio
March 1988
Abstract
This summary describes how information is encoded on Compact Disc (CD)
beginning with the physical pits and going up through higher levels of
data encoding to the structured multimedia information that is
possible with programs like HyperCard. This discussion is much
broader than any single standards document, e.g. the CD-Audio Red
Book, while omitting much of the detail needed only by drive
manufacturers.
Salient Characteristics
1. High information density -- With the density achievable using
optical encoding, the CD can contain some 540 megabytes of data on a
disc less than five inches in diameter.
2. Low unit cost -- Because CDs are manufactured by a well-developed
process similar to that used to stamp out LP records, unit cost in
large quantities is less than two dollars.
3. Read only medium -- CD-ROM is read only; it cannot be written on
or erased. It is an electronic publishing, distribution, and access
medium; it cannot replace magnetic disks.
4. Modest random access performance -- Due to optical read head mass
and data encoding methods, random access ("seek time") performance of
CD is better than floppies but not as good as magnetic hard disks.
5. Robust, removable medium -- The CD itself is comprised mostly of,
and completely coated by, durable plastic. This fact and the data
encoding method allow the CD to be resistant to scratches and other
handling damage. Media lifetime is expected to be long, well beyond
that of magnetic media such as tape. In addition, the optical servo
scanning mechanism allows CDs to be removed from their drives.
6. Multimedia storage -- Because all CD data is stored digitally, it
is inherently multimedia in that it can store text, images, graphics,
sound, and any other information expressed in digital form. Its only
limit in this area is the rate at which data can be read from the
disc, currently about 150 KBytes/second. This is sufficient for all
but uncompressed, full motion color video.
CD Data Hierarchy
Storing data on a CD may be thought of as occurring through a data
encoding hierarchy with each level built upon the previous one. At
the lowest level, data is physically stored as pits on the disc. It
is actually encoded by several low-level mechanisms to provide high
storage density and reliable data recovery. At the next level, it
organized into tracks which may be digital audio or CD-ROM. The High
Sierra specification then defines a file system built on CD-ROM
tracks. Finally, applications like HyperCard specify a content format
for files.
The Physical Medium
The Compact Disc itself is a thin plastic disk some 12 cm. in
diameter. Information is encoded in a plastic-encased spiral track
contained on the top of the disk. The spiral track is read optically
by a noncontact head which scans approximately radially as the disk
spins just above it. The spiral is scanned at a constant linear
velocity thus assuring a constant data rate. This requires the disc
to rotate at a decreasing rate as the spiral is scanned from its
beginning near the center of the disc to its end near the disc
circumference.
The spiral track contains shallow depressions, called pits, in a
reflective layer. Binary information is encoded by the lengths of
these pits and the lengths of the areas between them, called land.
During reading, a low power laser beam from the optical head is
focused on the spiral layer and is reflected back into the head. Due
to the optical characteristics of the plastic disc and the wavelength
of light used, the quantity of reflected light varies depending on
whether the beam is on land or on a pit. The modulated, reflected
light is converted to a radio frequency, raw data signal by a
photodetector in the optical head.
Low-level Data Encoding
To ensure accurate recovery, the disc data must be encoded to optimize
the analog-to-digital conversion process that the radio frequency
signal must undergo. Goals of the low level data encoding include:
1. High information density. This requires encoding that makes the
best possible use of the high, but limited, resolution of the laser
beam and read head optics.
2. Minimum intersymbol interference. This requires making the
minimum run length, i.e. the minimum number of consecutive zero bits
or one bits, as large as possible.
3. Self-clocking. To avoid a separate timing track, the data should
be encoded so as to allow the clock signal to be regenerated from the
data signal. This requires limiting the maximum run length of the
data so that data transitions will regenerate the clock.
4. Low digital sum value (the number of one bits minus the number of
zero bits). This minimizes the low frequency and DC content of the
data signal which permits optimal servo system operation.
A straightforward encoding would be to simply to encode zero bits as
land and one bits as pits. However, this does not meet goal (1) as
well as the encoding scheme actually used. The current CD scheme
encodes one bits as transitions from pit to land or land to pit and
zero bits as constant pit or constant land.
To meet goals (2) to (4), it is not possible to encode arbitrary
binary data. For example, the integer 0 expressed as thirty-two bits
of zero would have too long a run length to satisfy goal (3). To
accommodate these goals, each eight-bit byte of actual data is encoded
as fourteen bits of channel data. There are many more combinations of
fourteen bits (16,384) than there are of eight bits (256). To encode
the eight-bit combinations, 256 combinations of fourteen bits are
chosen that meet the goals. This encoding is referred to as
Eight-to-Fourteen Modulation (EFM) coding.
If fourteen channel bits were concatenated with another set of
fourteen channel bits, once again the above goals may not be met. To
avoid this possibility, three merging bits are included between each
set of fourteen channel bits. These merging bits carry no information
but are chosen to limit run length, keep data signal DC content low,
etc. Thus, an eight bit byte of actual data is encoded into a total
of seventeen channel bits: fourteen EFM bits and three merging bits.
To achieve a reliable self-clocking system, periodic synchronization
is necessary. Thus, data is broken up into individual frames each
beginning with a synchronization pattern. Each frame also contains
twenty-four data bytes, eight error correction bytes, a control and
display byte (carrying the subcoding channels), and merging bits
separating them all. Each frame is arranged as follows:
Sync Pattern 24 + 3 channel bits
Control and Display byte 14 + 3
Data bytes 12 * (14 + 3)
Error Correction bytes 4 * (14 + 3)
Data bytes 12 * (14 + 3)
Error Correction bytes 4 * (14 + 3)
TOTAL 588 channel bits
Thus, 192 actual data bits (24 bytes) are encoded as 588 channel bits.
Editorial: A CD physically has a single spiral track about 3 miles
long. CDs spin at about 500 RPM when reading near the center down to
about 250 RPM when reading near the circumference.
Disc with a 'c' or disk with a 'k'? A usage has emerged for these
terms: disk is used for eraseable disks (e.g. magnetic disks) while
disc is used for read-only (e.g. CD-ROM discs). One would presumably
call a frisbee a disc.
First Level Error Correction
Data errors can arise from production defects in the disk itself,
defects arising from subsequent damage to the disk, or jarring during
reading. A significant characteristic of these errors is that they
often occur in long bursts. This could be due, for example, to a
relatively wide mark on the disc that is opaque to the laser beam used
to read the disc. A system with two logical components called the
Cross Interleave Reed-Solomon Coding (CIRC) is employed for error
correction. The cross interleave component breaks up the long error
bursts into many short errors; the Reed-Solomon component provides the
error correction.
As each frame is read from the disc, it is first decoded from fourteen
channel bits (the three merging bits are ignored) into eight-bit data
bytes. Then, the bytes from each frame (twenty-four data bytes and
eight error correction bytes) are passed to the first Reed-Solomon
decoder which uses four of the error correction bytes and is able to
correct one byte in error out of the 32. If there are no
uncorrectable errors, the data is simply passed along. If there are
errors, the data is marked as being in error at this stage of
decoding.
The twenty-four data bytes and four remaining error correction bytes
are then passed through unequal delays before going through another
Reed-Solomon decoder. These unequal delays result in an interleaving
of the data that spreads long error bursts among many different passes
through the second decoder. The delays are such that error bursts up
to 450 bytes long can be completely corrected. The second
Reed-Solomon decoder uses the last four error correction bytes to
correct any remaining errors in the twenty-four data bytes. At this
point, the data goes through a de-interleaving process to restore the
correct byte order.
Subcoding Channels and Blocks
The eight-bit control and display byte in each frame carries the
subcoding channels. A subcoding block consists of 98 subcoding bytes,
and thus 98 of the 588-bit frames. A block then can contain 2352
bytes of data. Seventy-five blocks are read each second. With this
information, it is now straightforward to calculate that the CD data
rate is in fact correct for CD digital audio (CD-DA):
Required CD digital audio data rate: 44.1 K samples per second * 16
bits per sample * 2 channels = 1,411,200 bits/sec.
CD data rate: 8 bits per byte * 24 bytes per frame * 98 frames per
subcoding block * 75 subcoding blocks per second = 1,411,200 bits/sec.
The eight subcoding channels are labeled P through W and are encoded
one bit for each channel in a control and display byte. Channel P is
used as a simple music track separator. Channel Q is used for control
purposes and encodes information like track number, track type, and
location (minute, second, and frame number). During the lead-in track
of the disc, channel Q encodes a table of contents for the disk giving
track number and starting location. Standards have been proposed that
would use the remaining channels for line graphics and ASCII character
strings, but these are seldom used.
Track Types
Tracks can have two types as specified in the control bit field of
subchannel Q. The first type is CD digital audio (CD-DA) tracks. The
two-channel audio is sampled at 44.1 Khz with sixteen bit linear
sampling encoded as twos complement numbers. The sixteen bit samples
are separated into two eight-bit bytes; the bytes from each channel
alternate on the disc. Variations for audio tracks include
pre-emphasis and four track recording.
The other type of track specified by the subchannel Q control bit
field is the data track. These must conform to the CD-ROM standard
described below. In general, a disc can have a mix of CD digital
audio tracks and a CD-ROM track, but the CD-ROM track must come first.
Editorial: This first level error correction (the only type used for
CD Audio data) is extremely powerful. The CD specification allows for
discs to have up to 220 raw errors per second. Every one of these
errors is (almost always) perfectly corrected by the CIRC scheme for a
net error rate of zero. For example, our tests using Apple's CD-ROM
drive (which also plays audio) show that raw error rates are around
50-100 per second these days. Of course, these are perfectly
corrected, meaning that the original data is perfectly recovered. We
have tested flawed discs with raw rates up to 300 per second. Net
errors on all of these discs? Zero! I would expect a typical audio
CD player to perform similarly. Thus I expect this raw error rate to
have no audible consequences.
So why did I say "almost always" corrected above? Because a
sufficiently bad flaw may produce uncorrectable errors. These very
unusual errors are "concealed" by the player rather than corrected.
Note that this concealment is likely to be less noticeable than even a
single scratch on an LP. Such a flaw might be a really opaque finger
smudge; CDs do merit careful handling. On the two (and only two)
occasions I have found these, I simply sprayed on a little Windex
glass cleaner and wiped it off using radial strokes. This restored
the CDs to zero net errors.
One can argue about the quality of the process of conversion of analog
music to and from digital representation, but in the digital domain
CDs are really very, very good.
CD-ROM Data Tracks
Each CD-ROM data track is divided into individually addressable blocks
of 2352 data bytes, i.e. one subcoding block or 98 frames. A header
in each block contains the block address and the mode of the block.
The block address is identical to the encoding of minute, second, and
frame number in subcode channel Q. The modes defined in the CD-ROM
specification are:
Mode 0 -- all data bytes are zero.
Mode 1 -- (CD-ROM Data):
Sync Field - 12 bytes
Header Field - 4
User Data Field - 2048
Error Detection Code - 4
Reserved - 8
Error Correction - 276
Mode 2 -- (CD Audio or Other Data):
Sync Field - 12 bytes
Header Field - 4
User Data Field - 2048
Auxiliary Data Field - 288
Thus, mode 1 defines separately addressable, physical 2K byte data
blocks making CD-ROM look at this level very similar to other digital
mass storage devices.
Second Level Error Correction
An uncorrected error in audio data typically results in a brief, often
inaudible click during listening at worst. An uncorrected error in
other kinds of data, for example program code, may render a CD
unusable. For this reason, CD-ROM defines a second level of error
detection and error correction (EDC/ECC) for mode 1 data. The
information for the EDC/ECC occupies most of the auxiliary data field.
The error detection code is a cyclic redundancy check (CRC) on the
sync, header, and user data. It occupies the first four bytes of the
auxiliary data field and provides a very high probability that
uncorrected errors will be detected. The error correction code is
essentially the same as the first level error correction in that
interleaving and Reed-Solomon coding are used. It occupies the final
276 bytes of the auxiliary data field.
Editorial: This extra level of error correction for CD-ROM blocks is
one of the many reasons that CD-ROM drives are much more expensive
than consumer audio players. To perform this error correction quickly
requires substantial extra computing power (sometimes a dedicated
microprocessor) in the drive.
This is also one reason that consumer players like the Magnavoxes
which claim to be CD-ROM compatible (with their digital output jack on
the back) are useless for that purpose. They have no way of dealing
with the CD-ROM error correction. They also have no way for a
computer to tell them where to seek.
Another reason that CD-ROM drives are more expensive is that they are
built to be a computer peripheral rather than a consumer device, i.e.
like a combination race car/truck rather than a family sedan. One
story, probably apocryphal but not far from the truth, has it that a
major Japanese manufacturer tested some consumer audio players to
simulate computer use: they made them seek (move the optical head)
from the inside of the CD to the outside and back again. These are
called maximum seeks. The story says they managed to do this for
about 24 hours before they broke down. A CD-ROM drive needs to be
several orders of magnitude more robust. Fast and strong don't come
cheap.
The High Sierra File System Standard
Built on top of the addressable 2K blocks that the CD-ROM
specification defines, the next higher level of data encoding is a
file system that permits logical organization of the data on the CD.
This can be a native file system like the Macintosh Hierarchical File
System (HFS). Another alternative is the High Sierra (also known as
the ISO 9660) file standard, recently approved by the National
Information Standards Organization (NISO) and the International
Standards Organization (ISO), which defines a file system carefully
tuned to CD characteristics. In particular:
1. CDs have modest seek time and high capacity. As a result, the
High Sierra standard makes tradeoffs that reduce the number of seeks
needed to read a file at the expense of space efficiency.
2. CDs are read-only. Thus, concerns like space allocation, file
deletion, and the like are not addressed in the specification.
For High Sierra file systems, each individual CD is a volume. Several
CDs may be grouped together in a volume set and there is a mechanism
for subsequent volumes in a set to update preceding ones. Volumes can
contain standard file structures, coded character set file structures
for character encoding other than ASCII, or boot records. Boot
records can contain either data or program code that may be needed by
systems or applications.
High Sierra Directories and Files
The file system is a hierarchical one in which directories may contain
files or other directories. Each volume has a root directory which
serves as an ancestor to all other directories or files in the volume.
This dictates an overall tree structure for the volume.
A typical disadvantage in hierarchical systems is that to read a file
(which must be a leaf of the hierarchy tree) given its full path name,
it is necessary to begin at the root directory and search through each
of its ancestral directories until the entry for the file is found.
For example, given the path name
Wine Regions:America:California:Mendocino
three directories (the first three components of the path name) would
need to be searched. Typically, a separate seek would be required for
each directory. This would result in relatively poor performance.
To avoid this, High Sierra specifies that each volume contain a path
table in addition to its directories and files. The path table
describes the directory hierarchy in a compact form that may be cached
in computer memory for optimum performance. The path table contains
entries for the volume's directories in a breadth-first order;
directories with a common parent are listed in lexicographic order.
Each entry contains only the location of the directory it describes,
its name, and the location in the path table of its parent. This
mechanism allows any directory to be accessed with only a single CD
seek.
Directories contain more detailed information than the path table.
Each directory entry contains:
Directory or file location.
File length.
Date and time of creation.
Name of the file.
Flags:
Whether the entry is for a file or a directory.
Whether or not it is an associated file.
Whether or not it has records.
Whether or not it has read protection.
Whether or not it has subsequent extents.
Interleave structure of the file.
Interleaving may be used, for example, to meet realtime requirements
for multiple files whose contents must be presented simultaneously.
This would happen if a file containing graphic images were interleaved
with a file containing compressed sound that describes the images.
Files themselves are recorded in contiguous (or interleaved) blocks on
the disc. The read-only nature of CD permits this contiguous
recording in a straightforward manner. A file may also be recorded in
a series of noncontiguous extents with a directory entry for each
extent.
The specification does not favor any particular computer architecture.
In particular all significant, multibyte numbers are recorded twice,
once with the most significant byte first and once with the least
significant byte first.
Multimedia Information
Using the file system are applications that create and portray
multimedia information. While it is true that a CD can store anything
that a magnetic disk can store (and usually much more of it), CDs will
be used more for storing information than for storing programs. It is
the very large storage capacity of CDs coupled with their low cost
that opens up the possibilities for interactive, multimedia
information to be used in a multitude of ways.
Programs like HyperCard, with it's ease of authoring and broad
extensibility, are very useful for this purpose. Hypercard stacks,
with related information such as color images and sound, can be easily
and inexpensively stored on CDs despite their possibly very large
size.
Editorial: The High Sierra file system gets its name from the location
of the first meeting on it: the High Sierra Hotel at Lake Tahoe. It
is much more commonly referred to as ISO 9660, though the two
specifications are slightly different.
It has gotten very easy and inexpensive to make a CD-ROM disc (or
audio CD). For example, you can now take a Macintosh hard disk and
send it with $1500 to one of several CD pressers. They will send you
back your hard disk and 100 CDs with exactly the same content as
what's on your disk. This is the easy way to make CDs with capacity
up to the size of your hard disk (Apple's go up to 160 megabytes).
True, this is not a full CD but CDs don't need to be full. If you
have just 10 megabytes and need 100 copies, CDs may be the best way to
go.
If you are buying a CD-ROM drive, there are several factors you might
consider in making your choice. Two factors NOT to consider are
capacity and data rate. The capacity of all CD-ROM drives is
determined solely by the CD they are reading. Though you will see a
range of numbers in manufacturers' specs (e.g. 540, 550, 600, and 650
Mbytes), any drive can read any disc and so they are all fundamentally
the same. All CD-ROM drives read data at a net 150 Kbytes/sec for
CD-ROM data. Other data rates you may see may include error
correction data (not included in the net rate) or may be a mode 2 data
rate (faster than mode 1). All drives will be the same in all of
these specs.
End of article.

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From nntp.teleport.com!newsfeed.direct.ca!hunter.premier.net!news.mathworks.com!newsfeed.internetmci.com!vixen.cso.uiuc.edu!prairienet.org!dkrull Sun Aug 11 14:38:51 1996
Path: nntp.teleport.com!newsfeed.direct.ca!hunter.premier.net!news.mathworks.com!newsfeed.internetmci.com!vixen.cso.uiuc.edu!prairienet.org!dkrull
From: dkrull@prairienet.org (Don Krull)
Newsgroups: comp.lang.asm.x86
Subject: Re: DOS Sector => Physical Sector
Date: 5 Aug 1996 11:41:54 GMT
Organization: University of Illinois at Urbana
Lines: 14
Message-ID: <4u4mm2$2kn@vixen.cso.uiuc.edu>
References: <4tiluk$d8c@josie.abo.fi>
Reply-To: dkrull@prairienet.org (Don Krull)
NNTP-Posting-Host: firefly.prairienet.org
In a previous article, bhallstr@abo.fi asks:
> Does anyone have a formula for converting DOS Sectors to
> Physical Sectors (Head, Cylinder, Sector) such as used in
> INT 13h?
DOS_sector_num = BIOS_sector_num - 1 + Head_num*Sectors_per_track
+ Track_num*Sectors_per_track*Total_heads
BIOS_sector_num = 1 + (DOS_sector_num MOD Sectors_per_track)
Don
--

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NEC <20>PD765 - Floppy Disk Controller - 8272A
PS/2 FDC Diskette Status Register A at 3F0h
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> 3F0h PS/2 Disk Status Register A (read-only)
<20> <20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> direction
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> write protect
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> index
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> head 1 select
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> track 0
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> step
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> second drive installed
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> interrupt pending
PS/2 FDC Diskette Status Register B at 3F1h
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> 3F1h PS/2 Disk Status Register B (read-only)
<20> <20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> motor enable 0
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> motor enable 1
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> write enable
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> read data (toggles w/positive transition in -RD DATA)
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> write data (toggles w/positive transition in WR DATA)
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> drive select
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> reserved
FDC Digital Output Register at 3F2h (all systems)
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> port 3F2h (write only)
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> floppy drive select (0=A, 1=B, 2=floppy C, ...)
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1 = FDC enable, 0 = hold FDC at reset
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1 = DMA & I/O interface enabled (reserved PS/2)
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1 = turn floppy drive A motor on
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1 = turn floppy drive B motor on
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1 = turn floppy drive C motor on; (reserved PS/2)
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 1 = turn floppy drive D motor on; (reserved PS/2)
- used to control drive motors, drive selection, and feature enable
- PS/2 only uses bit 0 for floppy drive select; bit 1 is reserved
- PS/2 only uses bits 5 & 4 for motor enable; bits 7&6 are reserved
- all DOR bits are cleared during controller reset
FDC Main Status Register at 3F4h (all systems)
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> port 3F4h (read only)
<20> <20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> floppy drive 0 in seek mode/busy
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> floppy drive 1 in seek mode/busy
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> floppy drive 2 in seek mode/busy (reserved PS/2)
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> floppy drive 3 in seek mode/busy (reserved PS/2)
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDC read or write command in progress
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDC is in non-DMA mode
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> I/O direction; 1 = FDC to CPU; 0 = CPU to FDC
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> data reg ready for I/O to/from CPU (request for master)
FDC Command Status Register 0 at 3F5h (all systems)
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> Command Status Register 0 at port 3F5h
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> unit selected at interrupt (0=A, 1=B, 2=...)
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> head number at interrupt (head 0 or 1)
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> not ready on read/write or SS access to head 1
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> equipment check (see note)
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> set to 1 when FDD completes a seek command
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> last command status (see below)
Bits
76 Last Command Status
00 command terminated successfully
01 command execution started but terminated abnormally
10 invalid command issued
11 command terminated abnormally due to a change in state of
the Ready Signal from the FDC (reserved on PS/2)
- equipment check can occur if FDD signals a fault or track zero is
not found after 77 steps on a recalibrate command
- PS/2 only uses bits 1-0 for drive (values are 01b and 10b)
FDC Command Status Register 1 at 3F5h (all systems)
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> Command Status Register 1 at port 3F5h
<20> <20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> FDC cannot find ID address mark (see reg 2)
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> write protect detected during write
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDC cannot find sector ID
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> unused (always zero)
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> over-run; FDC not serviced in reasonable time
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> data error (CRC) in ID field or data field
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> unused (always zero)
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> end of cylinder; sector# greater than sectors/track
- bit 0 of Status Register 1 and bit 4 of Status Register 2 are
related and mimic each other
FDC Command Status Register 2 at 3F5h (all systems)
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> Command Status Register 2 at port 3F5h
<20> <20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> missing address mark in data field
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> bad cylinder, ID not found and Cyl Id=FFh
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> scan command failed, sector not found in cylinder
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> scan command equal condition satisfied
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> wrong cylinder detected
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> CRC error detected in sector data
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> sector with deleted data address mark detected
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> unused (always zero)
- bit 0 of Status Register 1 and bit 4 of Status Register 2 are
related and mimic each other
FDC Command Status Register 3 at 3F5h (FDD status, all systems)
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> Floppy Disk Drive Status at port 3F5h
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD unit selected status (0=A, 1=B, 2=...)
<20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD side head select status (0=head 0, 1=head 1)
<20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD two sided status signal
<20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD track zero status signal
<20> <20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD ready status signal
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD write protect status signal
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FDD fault status signal
PS/2 FDC Digital Input Register at 3F7h
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> 3F7h PS/2 Digital Input Register (read only)
<20> <20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD> high density select
<20> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> reserved
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> diskette change
PS/2 FDC Configuration Control Register at 3F7h
<09>7<EFBFBD>6<EFBFBD>5<EFBFBD>4<EFBFBD>3<EFBFBD>2<EFBFBD>1<EFBFBD>0<EFBFBD> 3F7h PS/2 Config. Control Register (write only)
<20> <20> <20> <20> <20> <20> <20><><EFBFBD><EFBFBD><EFBFBD> DRC1, DRC0 (see below)
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> reserved
DRC1 DRC0
0 0 500000 bit per second mode
0 1 reserved
1 0 250000 bit per second mode
1 1 reserved
- Digital Input Register is used to sense the state of the
(-diskette change) and the (-high density select) signals
- Configuration Control Register is used to set the transfer rate
FDC Programming Considerations
Three phases of command execution:
1. Command phase; commands are sent from the CPU to the FDC via
port 3F5h; bit 6 of the Status Register at 3F4h must be zero
2. Execution phase; FDC executes instruction & generates INT 6
3. Result phase; status and other information is available to CPU;
INT 6 sets bit 7 of BIOS Data Area location 40:3E which can
be polled for completion status
Example of a read operation:
1. turn disk motor on and set delay time for drive spin up
2. perform seek operation; wait for disk interrupt
3. prepare DMA chip to move data to memory
4. send read command and wait for transfer complete interrupt
5. read status information
6. turn disk motor off
Floppy Diskette Controller Operations (15 commands)
Read Data D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF SK 0 0 1 1 0
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: data length (if cmd byte 5==0)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Read Deleted Data D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF SK 0 1 1 0 0
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: data length (if cmd byte 5==0)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Write Data D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF 0 0 0 1 0 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: data length (if cmd byte 5==0)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Write Deleted Data D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF 0 0 1 0 0 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: data length (if cmd byte 5==0)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Read a Track D7 D6 D5 D4 D3 D2 D1 D0
(Diagnostic)
command byte 0: 0 MF SK 0 0 0 1 0
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: data length (if cmd byte 5==0)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Read ID D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: 0 MF 0 0 1 0 1 0
command byte 1: ? ? ? ? ? HD US1 US0
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Format a Track D7 D6 D5 D4 D3 D2 D1 D0
(Write Sector IDs)
command byte 0: 0 MF 0 0 1 1 0 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: bytes per sector
command byte 3: sectors per track
command byte 4: gap 3 length
command byte 5: filler pattern to write in each byte
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Scan Equal D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF SK 1 0 0 0 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: scan test (1=scan contiguous, 2=scan alternate)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Scan Low or Equal D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF SK 1 1 0 0 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: scan test (1=scan contiguous, 2=scan alternate)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Scan High or Equal D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: MT MF SK 1 1 1 0 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: cylinder number
command byte 3: head number
command byte 4: sector number
command byte 5: bytes per sector
command byte 6: end of track (last sector in track)
command byte 7: gap 3 length
command byte 8: scan test (1=scan contiguous, 2=scan alternate)
result byte 0: status register 0
result byte 1: status register 1
result byte 2: status register 2
result byte 3: cylinder number
result byte 4: head number
result byte 5: sector number
result byte 6: bytes per sector
Recalibrate D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: 0 0 0 0 0 1 1 1
command byte 1: ? ? ? ? ? 0 US1 US0
returns nothing
Sense Interrupt D7 D6 D5 D4 D3 D2 D1 D0
Status
command byte 0: 0 0 0 0 1 0 0 0
result byte 0: status register 0
result byte 1: present cylinder number
Specify Step & D7 D6 D5 D4 D3 D2 D1 D0
Head Load
command byte 0: 0 0 0 0 0 0 1 1
command byte 1: step rate time <20> head unload time
command byte 2: <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>head load time<6D><65><EFBFBD><EFBFBD><EFBFBD><EFBFBD> ND
returns nothing
Sense Drive D7 D6 D5 D4 D3 D2 D1 D0
Status
command byte 0: 0 0 0 0 0 1 0 0
command byte 1: ? ? ? ? ? HD US1 US0
result byte 0: status register 3
Seek D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: 0 0 0 0 1 1 1 1
command byte 1: ? ? ? ? ? HD US1 US0
command byte 2: new cylinder number
returns nothing
<20>PD765 Version D7 D6 D5 D4 D3 D2 D1 D0
command byte 0: ? ? ? 1 0 0 0 0
result byte 0: status register 0
90h = <20>PD765B; 80h = <20>PD765A or <20>PD765A-2
Invalid Command
result byte 0: status register 0 (value of 80h)
Key to Abbreviations
HD = Head Number Selected SK = SKip Deleted-data address mark
MT = Multi-Track US0 = drive select bit 0
MF = MFM mode US1 = drive select bit 1
ND = Non-DMA mode
Head Load Time = 2 to 254ms in 2ms increments
Head Unload Time = 16 to 240ms in 16ms increments
Step Rate Time = 1 to 16ms in 1ms increments
- PS/2 systems use the 8272A diskette controller which is software
and port compatible with the NEC <20>PD765
- accessed through ports 3F0h-3F7h; NEC <20>PD765 is accessed through
ports 3F2h, 3F4h and 3F5h; the 8272A uses ports 3F0h, 3F1h,
3F2h, 3F4h, 3F5h and 3F7h
- data, command and status registers are all accessed through
port 3F5h a register stack with one address presented to the bus
- bit 7 of BIOS Data Area byte 40:3E can be polled to determine
if a disk operation has completed; this bit is set by the
interrupt handler when the operation has completed; it should
be reset before continuing on with the next FDC operation

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These are from the Gospel according to Saint Peter:
Format Size Cyls Heads Sec/Trk FATs Sec/FAT Sec/Root Media
160K 5 1/4 40 1 8 2 ? ? FE
180K 5 1/4 40 1 9 2 ? 4 FC
320K 5 1/4 40 2 8 2 ? ? FF
360K 5 1/4 40 2 9 2 4 7 FD
1.2M 5 1/4 80 2 15 2 14 14 F9
720K 3 1/2 80 2 9 2 6 7 F9
1.44M 3 1/2 80 2 18 2 18 14 F0
2.88M 3 1/2 80 2 36 2 ? ? ?
Does anybody have the straight poop on the 2.88M variety? (I could
care less about the double-density, 5 1/4" formats.)
raster@indirect.com

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>Does anyone know how DOS generates serial-numbers for floppies?
Here are the details of the volume serial number:
The first part of the serial number is equal to the sum of the time
(seconds and hundredths of a second) and the date (month and day); The
second part of the serial number is equal to the sum of the time (hours
and minutes) and date (year), where all numbers are in hex. For
example, if the diskette is formatted at 8:32:43.65 on 7/21/1991, the
first part of the serial number will be 2B41+0715, or 3256; the second
part of the serial number will be 0820+07C7, or 0FE7.
Hope that this is of some help.
Ray

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From: datarec@inforamp.net (Nicholas Majors)
Subject: Chapter 1 - Technicians' Guide to Hard Disks (REPOST)
Date: 25 Mar 1995 18:45:09 GMT
========================================================================
Chapter 1 - TECHNICIANS' GUIDE TO PC HARD DISK SUBSYSTEMS
========================================================================
copyright (c) 1992, 1995
Nicholas Majors,
DATA RECOVERY LABS
(division of Data Recovery Services Inc) Voice : 1-416-510-6990
1315 Lawrence Avenue East - Unit 502 FAX : 1-416-510-6992
Don Mills, Ontario, Canada M3A 3R3 Email : datarec@the-wire.com
========================================================================
INTRODUCTION :
This booklet (now electronic) is published as a service of Data
Recovery Labs. Its purpose is to provide the fundamental knowledge of
concepts and terminology that is necessary to deal with the
complexities of hard disk subsystems. It is not a technical reference
guide and should not replace original documentation made available by
manufacturers.
Every day we meet and deal with technicians and support personnel who
install, upgrade and maintain hard drives, without knowing exactly
what they are and how they work. Gaining a working knowledge of disk
subsystems is not a simple task and requires much study - and -
experience. Don't expect any book, training course, or manual to make
you into an expert. However, if you read and understand most of this
material, you will be off to a fine start.
The principal author is Nick Majors. He has been in the industry
since 1979, designing and developing hardware and operating system
enhancements and performance tools. He is an experienced machine
language programmer and has provided technical training to support
personnel for some of Canada's leading banks, corporations, government
departments and PC service organizations. He is Manager of Technical
Services for Data Recovery Labs which he founded in 1989.
While this booklet deals primarily with PC and PC compatible
platforms, there is much information to benefit support personnel with
other hardware platforms.
Every effort has been made to ensure accuracy, but misprints and
ambiguities may still remain, so please use caution.
========================================================================
HISTORY AND OVERVIEW :
The original IBM PC, introduced in 1981, did not support any type of
hard drive. Program code in the BIOS did not recognize any such
device and early versions of DOS precluded mass storage by limiting
the maximum number of directory entries. This is not surprising when
you consider that the original 4.77 MHz PC came with 16 K of RAM,
expandable to 64 K on the motherboard. Even floppy drives and a disk
operating system were options to upgrade the built in cassette
recorder port and ROM basic.
To utilize a hard drive in a PC requires:
- a Hardware IRQ (interrupt request)
- I/O port addresses for the controller
- a DMA channel (now optional)
- low level program code
- a physical interface to the bus (expansion slot or built-in)
- operating system support
- sufficient power and cooling
After DOS 2 introduced the sub-directory system and support for mass
storage devices, companies started selling hard drives for the PC.
These were external cabinets that contained the disk itself, a
controller card, and a dedicated power supply (since the PC's 63.5 watts
were insufficient). Migrating from other architectures, these units
connected to the PC through cabling to an 8 bit adapter card that
plugged into an available expansion slot. These subsystems were
configured to use one of the available IRQ's, DMA channels, a range of
I/O ports, and program code that was made available through a device
driver loaded into memory after startup (booting from a floppy).
In 1983, the IBM XT (eXTended) was unveiled with its built-in 10 MB
fixed disk. IBM worked with a company (Xebec, I think) to take the
controller components normally located in the external cabinet and
build them right onto a bus interface card, creating what we commonly
call the "hard disk controller".
Program code was provided by a ROM chip on the controller card which
supplemented subroutines in the BIOS, and the internal power supply
was upgraded to 135 watts to provide power for the internally mounted
drive.
The XT design utilized :
- IRQ 5
- I/O port addresses 320-32f
- DMA channel 3
- Program Code from adapter ROM at c8000
- DOS 2.0 or higher
Several companies started manufacturing and selling similar
drive/controller packages with various improvements including higher
capacities, superior performance and built-in floppy controller
components on the same card (to save an expansion slot). These third
party subsystems could even be added to an original PC, so long as the
internal power supply was also upgraded.
In 1984, the IBM AT (Advanced Technology) brought a complete overhaul
to hard disk systems. Program code was included in the motherboard ROM
BIOS, eliminating the need for a ROM chip on the new 16 bit controller
card, and a higher quality drive improved access times. The system
included use of newly added higher IRQ's, eliminated the use of DMA
for hard drives, and changed the range of I/O addresses.
The AT design utilized :
- IRQ 14
- I/O port addresses 1f0-1f8
- DMA channel - none
- Program Code from motherboard ROM BIOS
- DOS 2.0 or higher
Hardware configuration details for the AT, including hard disk
parameters, were stored in a low power CMOS chip connected to a small
battery, eliminating many of the motherboard configuration dip
switches and jumpers. The battery allowed information to be
maintained while the computer was turned off and information could be
changed by running a setup program from disk.
The original AT supported 14 different drive types, recognizing
specific hard disks ranging from 10 to 112 MB. Any drive with
physical parameters that did not match one of these types needed a ROM
extension on the controller card or a device driver loaded during
boot-up.
DOS versions prior to 4.0 (or 3.31) did not support partitions larger
than 32 MB no matter how big a drive was. This was because of sector
numbering that could not exceed 16 bit values (up to 65,536 sectors).
To make a larger partition required the use of special software like
Ontrack's Disk Manager. This software was so popular that many drive
manufacturers shipped it with their product. Unfortunately, while
this offered one of the better solutions, it did pose compatibility
problems for many disk utilities because, in effect, you had a non-DOS
partition.
Many people opted instead to divide their drives into 32 MB partitions
creating a C: D: E: etc. up to the physical capacity. Prior to DOS
3.3, even this was not possible, because DOS did not recognize
extended partitions!
The number of drive types supported by CMOS has expanded to over 40
and most current BIOS's provide a user definable type to allow
parameters to match any drive. Most PC's today still rely on this
original CMOS drive type scheme to configure and control hard disks,
though many architectures and BIOS's have changed how the information
is stored and updated.
This inherently creates certain limiting factors, including a problem
with more than two hard drives and BIOS/OS limits to recognizing more
than 1024 cylinders, 16 heads and 63 sectors per track. Various
technologies must be used to translate non-compliant physical
geometries into logical parameters recognized by the system to
maintain compatibility with operating system and utility programs that
are tied to these limits.
With each sector holding 512 bytes of data this allows for drives no
larger than 504 MB.
(1024 X 16 X 63 = 1,032,192 sectors X 512 = 528,482,304 bytes)
To understand this limit, we have to examine how hard drives are
accessed by a PC.
Primarily, I/O commands are sent to the controller via a range of
reserved port addresses. This is a very complicated and tedious
process and the ROM BIOS includes a subroutine (INT 13) to perform
these tasks for you. The DOS operating system then has certain
functions that further simplify the process. They include INT 25/26
functions to read and write absolute sectors to the drive as well as
higher level functions (INT 21) to Open files, Close files, Write data
to files, etc. Most programs rely on these DOS functions to control
access to hard drives and DOS in turn calls the INT 13 BIOS
subroutines which do the actual I/O commands.
All of these subroutines are assembly language code that are loaded
into memory from either your BIOS chip(s) or Operating System files at
startup.
Assembly language routines store and manipulate values in registers
within the CPU. The lowest common denominator for INTEL based PC's is
16 bit registers. Any program or routine that wants to be backward
compatible, must use these base registers whether run on an 8088 or a
Pentium. This basic INT 13 is the backbone of PC compatibility and
uses 16 bit registers in the following way:
DX - 8 bits for head number - 8 bits for drive number
CX - 10 bits for cylinder number and 6 bits for sector number
The largest 10 bit number possible is 1023 hence the limit on cylinder
numbers (from 0-1023) and the largest 6 bit number is 63 (from 1-63)
allowing 63 sectors per track.
But note - the DX register allows a maximum of 255 heads, not the 16
that original specifications called for. This is what allows various
translation schemes to deal with drives up to 8 GB while remaining INT
13 compatible.
If the DX register allows 8 bits for drive number, shouldn't it be
able to control 255 drives instead of only two?
When the INT 13 sends commands to your controller, it must know the
physical geometry of the drive in question. During initialization of
the PC, values for disk types are read from CMOS and stored into an
area of RAM called the BIOS DATA AREA. Pointers to those entries are
stored in the Interrupt Vector Table (at addresses 0:104h and 0:118h).
The table only reserved pointers for two drives, so even if your CMOS
held more values, the standard routines wouldn't know how to deal with
them.
Why were the INT 13 routines so limited? They were written at a time
when 10 and 20 MB drives were the norm, and 120 MB was unbelievable.
They were designed to communicate with a specific controller
interface, the ST412/506 standard (WD1003 controller), and the specs
for passing parameters included only 10 bits for cylinders number, 4
bits for head number and a single bit for drive number.
Some of these limitations have been overcome in the past by replacing
the PC's INT 13 sub- routines with code that could recognize and deal
with different devices. That's why virtually all SCSI adapter cards
include a ROM chip and you must set the drive type to ZERO. In
effect, no standard drives installed for the motherboard BIOS to
control.
NetWare and other advanced Operating Systems use the drive type only
long enough to boot- up and then replace the INT 13 code with their
own device drivers. You then need to load a different .DSK file
written specifically for each type of controller.
In the past couple of years, many motherboard and controller BIOS's
have been enhanced to deal with ever increasing demands, but the
process of establishing new standards has led to continuing confusion
and compatibility problems.
========================================================================
END OF CHAPTER 1
========================================================================
COMING SOON - CHAPTER 2 - Inside Hard Drives and Controllers :
- Parts and Components
- also suggestions for must reading material
========================================================================
NOTICES & PERSONAL RANTS :
========================================================================
INTERNET APOLOGIES : The original artiticle, offering this booklet, was
posted Jan. 29, 1995. I have had lots of replies, BUT - all kinds of
people insist on replying by follow-up articles instead of private
Mail. This proved downright embarrassing! I only wanted E-MAIL
responses. Sorry for the clutter!
DISTRIBUTION : Chapters 1-2 will be sent by E-Mail to some 2,700
people who requested it and is being posted to various News groups.
The work to maintain a mailing list is much more trouble than it's
worth, therefore - future chapters will be posted to a select number of
New Groups and Bulletin Boards.
Files can be obtained by ftp. Look for "hdtech??.txt"
ftp site: archive.umich.edu in /msdos/info/disk
mirror : wuarchive.wustl.edu in /systems/ibmpc/umich.edu/info/disk
(Note - This mirror is not always up to date)
ftp site: ftp.wi.leidenuniv.nl in /pub/faqs
Also Daniel Tauritz has a home page with links to this document plus a
number of hard drive FAQs:
http://www.wi.leidenuniv.nl/~dtauritz/ata.html
If anyone specifically requires E-mail, send me a note with "e-mail
please" as the subject. I will be glad to accommodate them, assuming
it's a manageable number. I cannot provide hard copy or S-Mail.
RIGHTS : This material is copyright (C) 1992,1995 by Nicholas Majors
and Data Recovery Labs. Feel free to distribute it as either hard
copy, electronically, or by BBS - with full copyright credit to both.
COMMENTS & CRITICISM : I look forward to receiving suggestions,
improvements, additions, (and yes even compliments) to this material.
Please bear in mind who this has been written for - tech support
personnel, not end-users and not engineers or hardware designers.
========================================================================

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From: datarec@inforamp.net (Nicholas Majors)
Subject: Chapter 2 - Technicians' Guide to Hard Disks
Date: 25 Mar 1995 18:40:54 GMT
========================================================================
Chapter 2 - TECHNICIANS' GUIDE TO PC HARD DISK SUBSYSTEMS
========================================================================
copyright (c) 1992, 1995
Nicholas Majors,
DATA RECOVERY LABS
(division of Data Recovery Services Inc) Voice : 1-416-510-6990
1315 Lawrence Avenue East - Unit 502 FAX : 1-416-510-6992
Don Mills, Ontario, Canada M3A 3R3 Email : datarec@the-wire.com
========================================================================
Before we consider how to install, configure and maintain hard drives,
we need a basic understanding of drive construction and design concepts.
This chapter examines in some detail the parts and functional components
of hard drive subsystems.
(Note : A number of acronyms are used throughout this chapter and the
glossary for this booklet is not yet available. Therefore, I have
attached a brief set of definitions for some of the terminology.)
HARD DRIVES AND CONTROLLERS:
A hard drive subsystem is comprised of the following components:
1. The Hard Disk, with one or more boards (PCB) attached.
2. A Controller Mechanism, either on the hard disk PCB or on the bus
adapter within the PC.
3. Bus Adapter for interfacing the controller to the host PC.
4. Cables and Connectors to link it all together.
========================================================================
THE HARD DISK:
Within a sealed enclosure (Head Disk Assembly or HDA) are one or more
rigid platters that are "fixed" or non-removable. These are coated
with magnetically sensitized material and data can be written to and
read from the surface by means of electromagnetic read/write heads.
When powered up, the platters are constantly rotating (except for
certain pre-programmed sleep modes) and the heads are moved back and
forth across the surface to access different locations. This is a
sealed unit which should not be opened, except by qualified personnel in
a controlled, dust free environment.
The circuit board(s) attached to the outside of the HDA provide the
electronics needed for physical control of the motors within the sealed
unit. They interface the source of electrical power and control signals
to the disk assembly through various connectors and cables. Most boards
have some jumpers, dip switches and/or resistors that are used for
configuration purposes.
Functionally, these PCB's are separate from the Hard Disk Controller,
but many of the newer drives (IDE and SCSI) embed the controller chip
directly onto this board (as opposed to having it on the Bus adapter).
INSIDE THE HDA - PARTS OF A HARD DISK:
1. Disk Platter(s), separated by spacers and held together by a clamp.
2. Spindle shaft onto which platters are mounted.
3. Spindle motor for rotating the platters.
4. Electromagnetic read/write heads (usually, one per surface).
5. Access arms or armatures from which the heads are suspended.
6. Actuator for moving the arms (with heads attached).
7. Preamplifier circuitry to maximize read/write signals.
8. Air filter and pressure vent.
The Platters:
Most platters or disks are made of an aluminum alloy, though ceramic or
glass platters can also be found. The diameter is normally 2 1/2", 3
1/2" or 5 1/4" with a hole in the center for mounting onto the spindle
shaft. Thickness of the media can vary from less than 1/32 of an inch
to about 1/8 of an inch.
During manufacture the platters are coated with a magnetizable material.
Older drives used a ferrite compound applied by squirting a solution
onto the surface and rotating at high speeds to distribute the material
by centrifugal force. This process left a rust colored ferrite layer
which was then hardened, polished and coated with a lubricant.
Newer drives apply the magnetic layer by plating a thin metal film onto
the surface through galvanization or sputtering. These surfaces have a
shiny chrome-like appearance.
Spindle and Spindle Motors:
Most drives have several platters that are separated by disk spacers and
clamped to a rotating spindle that turns the platters in unison. A
direct drive, brushless spindle motor is built into the spindle or
mounted directly below it. (Sometimes this motor is visible from outside
of the sealed enclosure.) The spindle, and consequently the platters,
are rotated at a constant speed, usually 3,600 RPM, though newer models
have increased that to 4800, 5400, or 7,200.
The spindle motor receives control signals through a closed loop
feedback system that stabilizes to a constant rotation speed. Control
signals come from information written onto the surface(s) during
manufacture or with older drives, from physical sensors.
Read/Write Heads:
Since both sides of each platter are coated to provide separate
surfaces, there is normally one electromagnetic read/write head for each
side of each platter. Therefore, a drive with 4 platters would have 8
sides and 8 heads. Some drives use one side as a dedicated surface for
control signals leaving an odd number (5,7,etc.) of heads for actual
use.
Each head is mounted onto the end of an access arm and these arms (one
per surface) are moved in unison under the control of a single actuator
mechanism. When one head is over track 143, all the heads on all other
sides should be at the same location over their respective surfaces.
Generally speaking, only one of the heads is active at any given time.
There are some drives that can read or write from two or more heads at a
time, but while this has been common with main frame drives, it
represents a major design change for personal computers and the
technology is not yet widely used.
The spinning disk(s) create an air cushion over which the heads float.
Depending on design, this air buffer ranges from 2 to 15 microns. By
contrast, a smoke particle or finger print is about 30 microns in size!
The heads are not supposed to come into contact with the surface during
rotation. Only when powered off should the heads come to rest on the
surface, but this should be over a specific area of the surface,
reserved for that purpose. Most drives built since the late 1980's
employ an automatic parking feature which moves the heads to this
designated region and may even lock the heads there until powered up.
Head Actuators:
The head actuator is the positioning mechanism used to move the arms and
consequently the heads, back and forth over the surface. Once again,
earlier drives used a different method than is now common.
Originally, head positioning was controlled by a stepper motor that
rotated in either direction by reacting to stepper pulses and moving the
head assembly back and forth by means of a "rack and pinion" or by
spooling and unspooling a band attached to the actuator arms. Each
pulse moved the assembly over the surface in predefined steps or
detents. Each step represented a track location and data was expected
to be under the head. This design, still used for floppy drives, is not
suitable for current drive densities and is prone to alignment problems
caused by friction, wear and tear, heat deformation, and lack of
feedback information needed for correcting positioning error.
The more common voice coil actuator controls the movement of a coil
toward or away from a permanent magnet based upon the amount of current
flowing through it. The armatures are attached to this coil and move in
and out over the surface with it. This is a very precise method, but
also very sensitive. Any variation in the current can cause the head
assembly to change position and there are no pre-defined positions.
Inherently this is an analog system, with the exact amount of movement
controlled by the exact amount of current applied.
The actual position of the coil is determined by servo (or indexing)
information, which is written to the drive by the manufacturer.
Location is adjusted to different tracks by reading and reacting to
these control signals.
Internal Electronics:
There is surprisingly little circuitry found within the sealed HDA.
There are electrical and control wires for the spindle and head actuator
motors and the head assembly has flex cables with a preamplifier chip
often built onto it. This chip takes pulses from the heads (as close to
the source as possible) and cleans up and amplifies these signals before
transmission to components outside of the housing.
Air Filtering and Ventilation:
Minor wear of internal components and occasional contact of the heads
with the surface can cause microscopic particles to be loosened within
the HDA. A permanent air filter is mounted within the air stream to
remove these particles before they can cause damage to delicate
mechanisms.
Most drives also have a small vent to allow for minor air exchange from
outside of the housing. This allows for equalization of air pressure so
drives can be used in different environments without risk of imploding
or exploding.
========================================================================
CONTROLLERS AND BUS ADAPTERS:
The hard disk controller provides the logical link between a hard disk
unit and the program code within the host computer. It reacts to
requests from the computer by sending seek, read, write, and control
signals to the drive and must interpret and control the flow of data.
Data moving to and from the drive includes sector ID's, positioning
information and timing or clock signals. The controller must encode,
decode and separate this control information from actual data written to
or read from the drive.
Also, data is sent to and from the drive serially, in bit format, but
the CPU wants to recieve at least a byte (8 bits) at a time. The
controller must take bits (8 - 16 - or 32 at a time) and assemble them
into bytes, words, and doublewords that can be transferred to/from the
computer.
"OUR INDUSTRY MUST LOVE STANDARDS - WE HAVE THOUSANDS OF THEM!"
And so it is with hard disk controllers.
Controllers can be categorized in several different ways, by :
Basic computer design (PC/XT vs AT-286-386-486,etc)
- as mentioned in the first chapter, standard AT controllers use
different I/O addresses, IRQ and employ PIO as opposed to DMA.
Bus Architecture (8-16 bit ISA, 32 bit MCA/EISA/VLB/PCI, etc.)
- The adapter must be designed to interface with and use features of
available expansion spots in the host computer.
Controller Card vs Adapter
- The expansion board that plugs into the PC is commonly referred to
as a controller card, but for many drives (primarily IDE and SCSI)
the controller mechanism is built directly onto the drive PCB and
the expansion board in the PC (or built into motherboard) is
actually a Host/Bus adapter.
TROUBLESHOOTING TIP - If the BIOS reports "HDD CONTROLLER FAILURE" don't
assume the problem is with your AT/IO board. It might well be the drive
PCB that has failed.
Controller/Drive Interface
- Both drive and controller must communicate in the same 'language'
and several different standards for electrical properties and
logical meaning of signals have been established. These
include ST506/412, ESDI, SCSI, IDE(ATA/XTA) and EIDE(ATA2).
Data Encoding Method
- Determines how densely data can be packed onto a track. MFM
encoding is sufficient for only 17 x 512 byte sectors per track.
RLL permits up to 27 and variations of ARLL allow 34 or more
sectors per track. This recording density is a major determinant
of storage capacity, and with rotation speed and interleave are
critical factors for true data transfer capability.
Support for Translation
- Some controllers present different logical parameters to the PC
than the actual physical geometry of the drive.
Need for ROM Extension or Software Device Driver
- Additional program code is used to provide support for hard drives
when none exists (as in PC/XTs), to implement translation schemes
(as in ST506/RLL and ESDI designs), allow for non-standard devices
or features (SCSI), or for a combination of these (EIDE).
Below is a quick list of the major combinations that have been used in
PCs past and present. While I am sure many others could be added, these
are the ones I have come across over the years.
------------------------------------------------------------------------
Computer Bus Connection Interface Encoding Translate ROM
------------------------------------------------------------------------
PC/XT 8 bit ISA Controller ST506/412 MFM NO YES
PC/XT 8 bit ISA Controller ST506/412 RLL OPTION YES
AT 16 bit ISA Controller ST506/412 MFM NO NO
AT 16 bit MCA Controller ST506/412 MFM NO NO
AT 16 bit ISA Controller ST506/412 RLL OPTION YES
AT 16 bit MCA Controller ST506/412 RLL YES YES
AT 16 bit ISA Controller * ESDI (10 Mbps) RLL OPTION YES
AT 16 bit ISA Controller * ESDI (24 Mbps) ARLL OPTION YES
AT 16 bit MCA Controller ** ESDI (PS/2) RLL,ARLL YES YES
PC/XT 8 bit ISA Adapter SCSI RLL YES YES
AT 16 bit ISA Adapter SCSI RLL,ARLL YES YES
AT ?? bit MCA Adapter *** SCSI RLL,ARLL YES YES
AT 32 bit EISA Adapter SCSI RLL,ARLL YES YES
AT 32 bit VLB Adapter SCSI RLL,ARLL YES YES
AT 32 bit PCI Adapter SCSI RLL,ARLL YES YES
PC/XT 8 bit ISA Adapter IDE / XTA RLL OPTION YES
AT 16 Bit ISA Adapter IDE / ATA RLL,ARLL OPTION NO
AT 32 Bit VLB Adapter EIDE / ATA2 ARLL OPTION YES
AT 32 Bit PCI Adapter EIDE / ATA2 ARLL OPTION YES
* ESDI drives have some of the controller logic built onto
the hard drive PCB and some on the controller card.
** PS/2 ESDI uses the same physical interface as other ESDI
devices, but supports additional features specific to their
implementation.
*** 16 bit? 32 bit? Who knows? I have never been sure.
------------------------------------------------------------------------
Not to mention hundreds of other combinations to support different
interleaves, track buffers, hardware caching, bus mastering, error
correction schemes, SCSI I-II-III, optional floppy control, ESDI to SCSI
converters, ST506 to SCSI converters (etc., etc., etc.).
So, what does all this mean to you?
Specifically, don't be surprised if the drive you have in your left
hand, does not work correctly with the controller / adapter you have in
your right hand. Also, if controllers are changed it may affect
performance as well as the ability to access previously recorded data.
========================================================================
END OF CHAPTER 2
========================================================================
How to deal with some of this confusion will be addressed in
CHAPTER 3 - Installing and Configuring Hard Drives.
========================================================================
ADDITIONAL READING MATERIAL:
========================================================================
I have always had difficulty finding appropriate reading material to
recommend, but there are a few sources that I consider a must for
technicians and support personnel.
First, a number of Internet Newsgroups have exceptional FAQ's
(Frequently Asked Questions) which are updated and posted on a regular
basis. These include:
"YET ANOTHER ATA-2/FAST-ATA/EIDE FAQ"
by John Wehman and Peter Herweijer
Newsgroup : comp.sys.ibm.hardware.storage
"BIOS TYPES"
by Hale Landis
Newsgroup : comp.sys.ibm.hardware.storage
"SCSI FAQ - 2 Parts"
by Gary A. Field
Newsgroup : comp.periphs.scsi
While bookstores are full of titles, most of them simply provide a
rehash of basics. The following two books are an important part of my
library because they cover much more than the usual:
"THE INDISPENSABLE PC HARDWARE BOOK" by Hans-Peter Messmer (1994)
Addison-Wesley Publishing Company,
ISBN - 0-201-62424-9
"THE UNDOCUMENTED PC" by Frank Van Gilluwe (1994)
Addison-Wesley Publishing Company,
ISBN - 0-201-62277-7
Other books well worth the read include:
"THE HARD DISK SURVIVAL GUIDE" by Mark Minasi (1991)
Sybex Inc.,
ISBN - 0-89588-799-1
A little dated, but full of useful information. Hopefully there is a
revised and updated version.
"OFFICIAL SPINRITE II AND HARD DISK COMPANION" by J. M. Goodman, (1990)
IDG Books Worldwide, Inc.,
ISBN - 878058-08-8
Current advances are not covered, but great explanation of drive basics.
"HARD DRIVE BIBLE" by Martin Bodo (1993)
Corporate Systems Center (CSC)
My copy is the sixth edition from April, 1993. The first 50 pages of
the book should be of interest (though not always clearly organized).
The balance of the book (150 pages) is a listing of drive types and
jumper settings. It's quite good, but keeping something like that
updated is virtually impossible.
WARNING - DO NOT BUY - "The Data Recovery Bible" by Pamela Kane.
Poorly organized material, most of which has nothing to do with data
recovery. Waste of a good title if you ask me!
========================================================================
ACRONYM DEFINITIONS:
========================================================================
IRQ (Interrupt Request) - Lines on the bus used to signal hardware
interrupts.
I/O (Input Output) - Peripherals accessible by the CPU through registers
at specific I/O addresses (or I/O ports).
PIO (Programmed Input Output) - Exchange of data between memory and
peripherals by means of Input Output commands.
DMA (Dynamic Memory Access) - Transferring data directly between memory
and peripherals without going through the CPU.
BUS ARCHITECTURES:
ISA (Industry Standard Architecture) - 8 bit and 16 bit expansion slots
used by PC, XT, and AT designs. Often called IBM Standard Architecture.
EISA (Extended Industry Standard Architecture) - Developed by several
independent manufacturers (Compaq, AST, Zenith, Tandy, etc.) to
standardize 32 bit operation and combat IBM's MCA.
MCA (Micro Channel Architecture) - Expansion bus introduced by IBM in
1987, used by some (but not all) PS/2 models.
PCI (Peripheral Component Interconnect) - High speed bus developed by
Intel to support the demands of Pentium and 486 based computers.
VLB (VESA Local Bus) - High speed, 32 bit extension to the ISA bus
promoted by the VESA (Video Electronics Standards Association).
DRIVE INTERFACES:
ST506/412 - Standard interface used on XT and AT drives and controllers.
Originally developed by Seagate Technologies to support their ST506
(5 MB) and ST412 (10 MB) drives. The entire controller mechanism is
located on a controller card and communications between the drive and
controller flow over 2 ribbon cables - one for drive control and one for
data.
ESDI (Enhanced Small Device Interface) - Developed by Maxtor in the
early 1980's as an upgrade and improvement to the ST506 design. While
the drive does not have an embedded controller, one of the most critical
functions ,encoding-decoding, is performed on the drive. This allows
for faster communications and higher drive capacities. Uses the same
cabling as ST506 interface, but carries different signals on each line.
SCSI (Small Computer System Interface) - Based on an original design by
Shugart Associates, SCSI is not specifically a drive interface, but a
method of allowing different devices to communicate with a PC. For hard
drives the entire controller is built onto the drive PCB, allowing for
very high speed transfers to and from the drive. Fully interpreted,
parallel data is then transferred to and from the PC by way of a single
cable through a bus interface that has configured the device as a hard
drive.
IDE (Integrated Drive Electronics) - A technology pioneered by Compaq
and Conner that embedded a controller onto the hard disk PCB while
maintaining compatibility with the register level commands sent by the
computer's INT 13 routines. IDE drives are configured and appear to the
computer like standard ST506 drives.
ATA (AT Attachment) - Implementation of the IDE design with a 16 bit AT
style controller on board the drive.
XTA (XT Attachment) - Rarely used implementation of IDE with an
integrated 8 bit XT controller.
ATA-2 - Enhancement to the AT Attachment standard to provide for
considerable performance improvement and more sophisticated drive
identification.
EIDE (Enhanced IDE) and FAST-ATA - Various implementations of the ATA-2
standard as marketed by Western Digital (EIDE) and Seagate/Quantum
(FAST-ATA).
DATA ENCODING SCHEMES
MFM (Modified Frequency Modulation) - Common technique used to encode
the magnetic fluxes recorded on a drive into data. Still used on floppy
drives and most original XT and AT systems. Notice that most drive
types supported by the motherboard BIOS have 17 sectors per track. This
is the standard density for MFM encoding.
RLL (Run Length Limited) - Encoding method that allows 50% more
information to be recorded on a track than MFM. Accomplished by
recording larger representations for every byte, but able to pack them
more tightly onto the surface, because of fewer actual flux changes.
Often called 2,7 RLL because the recording scheme involves patterns with
no more than 7 successive zeros and no less than two.
ARLL (Advanced Run Length Limited) - More complex yet powerful
derivatives of the RLL scheme. Include 1,7 and 3,9 encoding. Most
every new drive made today uses some form of RLL or ARLL encoding.
========================================================================

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; Reading the harddisk using ports!
; +-------------------------------+ by qark
;
;
; This took me months to get working but I finally managed it.
;
; This code only works for the 286+ so you must detect for 8088's somewhere
; in your code.
;
; Technical Information on the ports:
; Port Read/Write Misc
; ------ ------------ -------------------------------------------------
; 1f0 r/w data register, the bytes are written/read here
; 1f1 r error register (look these values up yourself)
; 1f2 r/w sector count, how many sectors to read/write
; 1f3 r/w sector number, the actual sector wanted
; 1f4 r/w cylinder low, cylinders is 0-1024
; 1f5 r/w cylinder high, this makes up the rest of the 1024
; 1f6 r/w drive/head
; bit 7 = 1
; bit 6 = 0
; bit 5 = 1
; bit 4 = 0 drive 0 select
; = 1 drive 1 select
; bit 3-0 head select bits
; 1f7 r status register
; bit 7 = 1 controller is executing a command
; bit 6 = 1 drive is ready
; bit 5 = 1 write fault
; bit 4 = 1 seek complete
; bit 3 = 1 sector buffer requires servicing
; bit 2 = 1 disk data read corrected
; bit 1 = 1 index - set to 1 each revolution
; bit 0 = 1 previous command ended in an error
; 1f7 w command register
; commands:
; 50h format track
; 20h read sectors with retry
; 21h read sectors without retry
; 22h read long with retry
; 23h read long without retry
; 30h write sectors with retry
; 31h write sectors without retry
; 32h write long with retry
; 33h write long without retry
;
; Most of these should work on even non-IDE hard disks.
; This code is for reading, the code for writing is the next article.
mov dx,1f6h ;Drive and head port
mov al,0a0h ;Drive 0, head 0
out dx,al
mov dx,1f2h ;Sector count port
mov al,1 ;Read one sector
out dx,al
mov dx,1f3h ;Sector number port
mov al,1 ;Read sector one
out dx,al
mov dx,1f4h ;Cylinder low port
mov al,0 ;Cylinder 0
out dx,al
mov dx,1f5h ;Cylinder high port
mov al,0 ;The rest of the cylinder 0
out dx,al
mov dx,1f7h ;Command port
mov al,20h ;Read with retry.
out dx,al
still_going:
in al,dx
test al,8 ;This means the sector buffer requires
;servicing.
jz still_going ;Don't continue until the sector buffer
;is ready.
mov cx,512/2 ;One sector /2
mov di,offset buffer
mov dx,1f0h ;Data port - data comes in and out of here.
rep insw
; ------
mov ax,201h ;Read using int13h then compare buffers.
mov dx,80h
mov cx,1
mov bx,offset buffer2
int 13h
mov cx,512
mov si,offset buffer
mov di,offset buffer2
repe cmpsb
jne failure
mov ah,9
mov dx,offset readmsg
int 21h
jmp good_exit
failure:
mov ah,9
mov dx,offset failmsg
int 21h
good_exit:
mov ax,4c00h ;Exit the program
int 21h
readmsg db 'The buffers match. Hard disk read using ports.$'
failmsg db 'The buffers do not match.$'
buffer db 512 dup ('V')
buffer2 db 512 dup ('L')
;
; Writing to the hard disk using the ports! by qark
; +---------------------------------------+
;
; The only differences between reading and writing using the ports is
; that 30h is sent to the command register, and instead of INSW you
; OUTSW.
;
; I chose to write to sector 2 because some idiot would trash their MBR
; by running this.
;
mov dx,1f6h ;Drive and head port
mov al,0a0h ;Drive 0, head 0
out dx,al
mov dx,1f2h ;Sector count port
mov al,1 ;Write one sector
out dx,al
mov dx,1f3h ;Sector number port
mov al,2 ;Wrote to sector two
out dx,al
mov dx,1f4h ;Cylinder low port
mov al,0 ;Cylinder 0
out dx,al
mov dx,1f5h ;Cylinder high port
mov al,0 ;The rest of the cylinder 0
out dx,al
mov dx,1f7h ;Command port
mov al,30h ;Write with retry.
out dx,al
oogle:
in al,dx
test al,8 ;Wait for sector buffer ready.
jz oogle
mov cx,512/2 ;One sector /2
mov si,offset buffer
mov dx,1f0h ;Data port - data comes in and out of here.
rep outsw ;Send it.
; ------------
mov ax,201h ;We'll read in sector 2 using
mov bx,offset buffer2 ;int13h and see if we are successful.
mov cx,2
mov dx,80h
int 13h
mov cx,512
mov si,offset buffer
mov di,offset buffer2
repe cmpsb ;Compare the buffers.
jne failure
mov ah,9
mov dx,offset write_msg
int 21h
jmp w_exit
failure:
mov ah,9
mov dx,offset fail
int 21h
w_exit:
mov ax,4c00h ;Exit the program
int 21h
write_msg db 'Sector two written to using the ports.$'
fail db 'Writing using ports failed.$'
buffer db 512 dup ('A')
buffer2 db 512 dup ('D')

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; ========================================================================== ;
; IDEHDC.asm ;
; Direct disk I/O module for IDE disk controllers. ;
; Written by Alan Martin. ;
; Note - this code doesn't use interrupts! ;
; ========================================================================== ;
idehdc segment use16 'CODE' ; Direct disk I/O code segment.
; Initialize segment.
assume cs:idehdc ; Initial segment assumptions.
.386 ; Assume 386+ code is valid.
; Stack addressing equates.
_ax equ word ptr bp+001Ch ; Saved AX value.
_al equ byte ptr bp+001Ch ; Saved AL value.
_ah equ byte ptr bp+001Dh ; Saved AH value.
_bx equ word ptr bp+0010h ; Saved BX value.
_bl equ byte ptr bp+0010h ; Saved BL value.
_bh equ byte ptr bp+0011h ; Saved BH value.
_cx equ word ptr bp+0018h ; Saved CX value.
_cl equ byte ptr bp+0018h ; Saved CL value.
_ch equ byte ptr bp+0019h ; Saved CH value.
_dx equ word ptr bp+0014h ; Saved DX value.
_dl equ byte ptr bp+0014h ; Saved DL value.
_dh equ byte ptr bp+0015h ; Saved DH value.
delay macro x ; Long delay (for 400ns transition).
local @loop ; Local labels.
push cx ; Save CX.
mov cx,x ; Get repeat count.
@loop: loop @loop ; Loop X times.
pop cx ; Restore CX.
endm ; End of DELAY macro.
hdcwait macro ; Wait for HDC to finish commands.
local @loop,@ok,@err ; Local labels.
push ax ecx dx ; Save registers.
mov ecx,00040000h ; 1s delay on 486DX-50.
mov dx,01F7h ; HDC status register.
in al,dx ; Read status.
test al,80h ; Is the HDC busy?
jz @ok ; If not, end immediately.
@loop: in al,dx ; Read status.
delay 000Ah ; 50-100 clock delay.
test al,80h ; Is the HDC busy?
jz @ok ; If not, end loop.
loopd @loop ; Otherwise, continue.
pop dx ecx ax ; Restore registers.
stc ; Set CF.
jmp @err ; Exit with error.
@ok: pop dx ecx ax ; Restore registers.
clc ; Clear CF.
@err:
endm ; End of HDCWAIT macro.
; ------------------------------------------ ;
; IOREAD - Read sectors through direct I/O. ;
; Input.: AX=cylinder number ;
; BH=head number; BL=sector number ;
; CH=# of sectors; CL=drive (0 or 1) ;
; DS:DX->buffer for sectors ;
; Output: CF=0 (OK) or 1 (Error) ;
; AL=error code or 0 if no error. ;
; AH=device error code if applicable.;
; Errors: AL=0 - No error. ;
; 1 - Controller busy or absent. ;
; 2 - Drive not ready. ;
; 3 - Drive not ready for read. ;
; 4 - Device error: ;
; AH, bit 0: Address mark not found. ;
; 1: Track 0 not found. ;
; 2: Write fault. ;
; 4: Sector not found. ;
; 6: Error in data. ;
; 7: Sector marked bad. ;
; Note: There may be errors if a read is ;
; across a cylinder (or sometimes even ;
; a head) boundary. ;
; ------------------------------------------ ;
ioread proc far ; Read sectors through direct I/O.
pushad ; Save all registers.
mov bp,sp ; Address the stack.
push ds es ; Save segments.
in al,0A1h ; Get PIC 2 mask.
push ax ; Save it.
or al,40h ; Disable IRQ 14.
out 0A1h,al ; Set PIC 2 mask.
hdcwait ; Wait for HDC not busy.
jnc ir_ok0 ; Continue if not busy.
mov al,01h ; Error 1: Controller busy...
mov [_al],al ; .
jmp ir_err ; ...done.
ir_ok0:mov al,[_bh] ; Get head number.
mov ah,[_cl] ; Get drive number.
and ax,010Fh ; Mask out extra bits.
shl ah,04h ; Adjust AH.
or al,ah ; Combine data.
or al,0A0h ; Set 512 bytes + ECC.
mov dx,01F6h ; Write drive/head numbers...
out dx,al ; ...done.
hdcwait ; Wait for HDC not busy.
jnc ir_ok1 ; Continue if not busy.
mov al,01h ; Error 1: Controller busy...
mov [_al],al ; .
jmp ir_err ; ...done.
ir_ok1:mov ecx,000C0000h ; 3s delay.
mov dx,01F7h ; HDC status register.
ir_l1: in al,dx ; Read status.
test al,40h ; Drive ready?
jnz ir_ok2 ; Continue if so.
loopd ir_l1 ; Loop for 3s.
mov al,02h ; Error 2: Drive not ready...
mov [_al],al ; .
jmp ir_err ; ...done.
ir_ok2:test al,10h ; Drive ready for read?
jnz ir_ok3 ; Continue if so.
loopd ir_l1 ; Loop for 3s.
mov al,03h ; Error 3: Cannot read data...
mov [_al],al ; .
jmp ir_err ; ...done.
ir_ok3:mov al,10h ; Set to >8 heads...
mov dx,03F6h ; .
out dx,ax ; ...done.
mov dx,01F2h ; Write read parameters...
mov al,[_ch] ; .
out dx,al ; .
inc dx ; .
mov al,[_bl] ; .
out dx,al ; .
inc dx ; .
mov al,[_al] ; .
out dx,al ; .
inc dx ; .
mov al,[_ah] ; .
out dx,al ; .
inc dx ; .
mov al,[_bh] ; .
mov ah,[_cl] ; .
and ax,010Fh ; .
shl ah,04h ; .
or al,ah ; .
or al,0A0h ; .
out dx,al ; ...done.
mov dx,01F1h ; Write Precompensation = 0...
xor al,al ; .
out dx,al ; ...done.
hdcwait ; Wait for HDC not busy.
jnc ir_ok4 ; Continue if not busy.
mov al,01h ; Error 1: Controller busy...
mov [_al],al ; .
jmp ir_err ; ...done.
ir_ok4:xor cx,cx ; Get sector count...
mov cl,[_ch] ; ...done.
push ds ; Put DS in ES...
pop es ; ...done.
mov di,[_dx] ; Get offset.
mov dx,01F7h ; Send read command...
mov al,20h ; .
out dx,al ; ...done.
ir_l2: mov dx,01F7h ; Get status port.
delay 000Ah ; Delay for >400ns.
in al,dx ; Get status.
test al,80h ; Busy?
jnz ir_l2 ; Loop if so.
test al,29h ; Loop if no change...
jz ir_l2 ; ...done.
test al,08h ; Ready for data?
jnz ir_rda ; If so, read it.
test al,21h ; Error in command?
jnz ir_dev ; If so, return device error.
jmp ir_l2 ; Continue loop.
ir_rda:push cx ; Save CX.
mov cx,0100h ; Repeat count.
mov dx,01F0h ; 16-bit transfer port.
rep insw ; Read data.
pop cx ; Restore CX.
loop ir_l2 ; Loop until done.
mov al,12h ; Deactivate controller...
mov dx,03F6h ; .
out dx,ax ; ...done.
mov al,00h ; No error - return 0...
mov [_al],al ; ...done.
pop ax ; Reset PIC 2 mask...
out 0A1h,al ; ...done.
clc ; No error: CF=0.
pop es ds ; Restore segments.
popad ; Restore all registers.
ret ; Return (far).
ir_dev:mov al,04h ; Error 4: Device fault...
mov [_al],al ; ...done.
mov dx,01F1h ; Get error code...
in al,dx ; .
mov [_ah],al ; ...done.
mov dx,01F6h ; Recalibrate head...
mov al,[_bh] ; .
mov ah,[_cl] ; .
and ax,010Fh ; .
shl ah,04h ; .
or al,ah ; .
or al,0A0h ; .
out dx,al ; .
inc dx ; .
mov al,10h ; .
out dx,al ; ...done.
hdcwait ; Wait for HDC not busy.
mov al,12h ; Deactivate controller...
mov dx,03F6h ; .
out dx,ax ; ...done.
ir_err:pop ax ; Reset PIC 2 mask...
out 0A1h,al ; ...done.
stc ; Error: CF=1.
pop es ds ; Restore segments.
popad ; Restore all registers.
ret ; Return (far).
ioread endp ; End of IOREAD procedure.
; ------------------------------------------ ;
; IOWRITE - Write sectors through direct I/O.;
; Input.: AX=cylinder number ;
; BH=head number; BL=sector number ;
; CH=# of sectors; CL=drive (0 or 1) ;
; DS:DX->buffer for sectors ;
; Output: CF=0 (OK) or 1 (Error) ;
; AL=error code or 0 if no error. ;
; AH=device error code if applicable.;
; Errors: AL=0 - No error. ;
; 1 - Controller busy or absent. ;
; 2 - Drive not ready. ;
; 3 - Drive not ready for write. ;
; 4 - Device error: ;
; AH, bit 0: Address mark not found. ;
; 1: Track 0 not found. ;
; 2: Write fault. ;
; 4: Sector not found. ;
; 6: Error in data. ;
; 7: Sector marked bad. ;
; Note: There may be errors if a write is ;
; across a cylinder (or sometimes even ;
; a head) boundary. ;
; ------------------------------------------ ;
iowrite proc far ; Write sectors through direct I/O.
pushad ; Save all registers.
mov bp,sp ; Address the stack.
push ds es ; Save segments.
in al,0A1h ; Get PIC 2 mask.
push ax ; Save it.
or al,40h ; Disable IRQ 14.
out 0A1h,al ; Set PIC 2 mask.
hdcwait ; Wait for HDC not busy.
jnc iw_ok0 ; Continue if not busy.
mov al,01h ; Error 1: Controller busy...
mov [_al],al ; .
jmp iw_err ; ...done.
iw_ok0:mov al,[_bh] ; Get head number.
mov ah,[_cl] ; Get drive number.
and ax,010Fh ; Mask out extra bits.
shl ah,04h ; Adjust AH.
or al,ah ; Combine data.
or al,0A0h ; Set 512 bytes + ECC.
mov dx,01F6h ; Write drive/head numbers...
out dx,al ; ...done.
hdcwait ; Wait for HDC not busy.
jnc iw_ok1 ; Continue if not busy.
mov al,01h ; Error 1: Controller busy...
mov [_al],al ; .
jmp iw_err ; ...done.
iw_ok1:mov ecx,000C0000h ; 3s delay.
mov dx,01F7h ; HDC status register.
iw_l1: in al,dx ; Read status.
test al,40h ; Drive ready?
jnz iw_ok2 ; Continue if so.
loopd iw_l1 ; Loop for 3s.
mov al,02h ; Error 2: Drive not ready...
mov [_al],al ; .
jmp iw_err ; ...done.
iw_ok2:test al,10h ; Drive ready for write?
jnz iw_ok3 ; Continue if so.
loopd iw_l1 ; Loop for 3s.
mov al,03h ; Error 3: Cannot write...
mov [_al],al ; .
jmp iw_err ; ...done.
iw_ok3:mov al,10h ; Set to >8 heads...
mov dx,03F6h ; .
out dx,ax ; ...done.
mov dx,01F2h ; Write write parameters...
mov al,[_ch] ; .
out dx,al ; .
inc dx ; .
mov al,[_bl] ; .
out dx,al ; .
inc dx ; .
mov al,[_al] ; .
out dx,al ; .
inc dx ; .
mov al,[_ah] ; .
out dx,al ; .
inc dx ; .
mov al,[_bh] ; .
mov ah,[_cl] ; .
and ax,010Fh ; .
shl ah,04h ; .
or al,ah ; .
or al,0A0h ; .
out dx,al ; ...done.
mov dx,01F1h ; Write Precompensation = 0...
xor al,al ; .
out dx,al ; ...done.
hdcwait ; Wait for HDC not busy.
jnc iw_ok4 ; Continue if not busy.
mov al,01h ; Error 1: Controller busy...
mov [_al],al ; .
jmp iw_err ; ...done.
iw_ok4:xor cx,cx ; Get sector count...
mov cl,[_ch] ; ...done.
mov si,[_dx] ; Get offset.
mov dx,01F7h ; Send write command...
mov al,30h ; .
out dx,al ; ...done.
iw_l2: mov dx,01F7h ; Get status port.
delay 000Ah ; Delay for >400ns.
in al,dx ; Get status.
test al,80h ; Busy?
jnz iw_l2 ; Loop if so.
test al,29h ; Loop if no change...
jz iw_l2 ; ...done.
test al,08h ; Ready for data?
jnz iw_wda ; If so, write it.
test al,21h ; Error in command?
jnz iw_dev ; If so, return device error.
jmp iw_l2 ; Continue loop.
iw_wda:push cx ; Save CX.
mov cx,0100h ; Repeat count.
mov dx,01F0h ; 16-bit transfer port.
rep outsw ; Write data.
pop cx ; Restore CX.
loop iw_l2 ; Loop until done.
mov al,12h ; Deactivate controller...
mov dx,03F6h ; .
out dx,ax ; ...done.
mov al,00h ; No error - return 0...
mov [_al],al ; ...done.
pop ax ; Reset PIC 2 mask...
out 0A1h,al ; ...done.
clc ; No error: CF=0.
pop es ds ; Restore segments.
popad ; Restore all registers.
ret ; Return (far).
iw_dev:mov al,04h ; Error 4: Device fault...
mov [_al],al ; ...done.
mov dx,01F1h ; Get error code...
in al,dx ; .
mov [_ah],al ; ...done.
mov dx,01F6h ; Recalibrate head...
mov al,[_bh] ; .
mov ah,[_cl] ; .
and ax,010Fh ; .
shl ah,04h ; .
or al,ah ; .
or al,0A0h ; .
out dx,al ; .
inc dx ; .
mov al,10h ; .
out dx,al ; ...done.
hdcwait ; Wait for HDC not busy.
mov al,12h ; Deactivate controller...
mov dx,03F6h ; .
out dx,ax ; ...done.
iw_err:pop ax ; Reset PIC 2 mask...
out 0A1h,al ; ...done.
stc ; Error: CF=1.
pop es ds ; Restore segments.
popad ; Restore all registers.
ret ; Return (far).
iowrite endp ; End of IOWRITE procedure.
; Clean up segment.
assume nothing ; Remove segment assumptions.
idehdc ends ; End of direct I/O segment.
; ========================================================================== ;

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<STYLE MEDIA="screen">
#bodytext { font-family: Verdana, Arial, Helvetica;font-size: 9pt; line-height: 125%;}
</STYLE>
<STYLE MEDIA="print">
#bodytext {display: all; margin-left: 90px; margin-right: 20px; font-family: Times; font-size: 11pt; line-height: 112%;}
</STYLE>
<FONT FACE="Verdana, Arial, Helvetica" SIZE=1><blockquote><div id="bodytext">
<!-- XXXXXXXXXXXXXXXXX PAGE TITLE: XXXXXXXXXXXXXXXXXXXXX -->
<h3 class=main>Media Status Notification Support Specification for SCSI and ATAPI Devices, Version 0.1</h3>
<!-- XXXXXXXXXXXXXXXXX START TOC: XXXXXXXXXXXXXXXXXXXXXX -->
<DL class=contents>
<DT class=contents><B>Contents:</B></DT>
<DD class=contents><a class=contents href="#Introduction">Introduction</a></DD>
<DD class=contents><a class=contents href="#Enabling">Enabling and Disabling Media Status Notification Support</a></DD>
<DD class=contents><a class=contents href="#Returning">Returning Media Status</a></DD>
<DD class=contents><a class=contents href="#Reporting">Reporting Media Status Changes</a></DD>
<DD class=contents><a class=contents href="#SCSI">SCSI Compatibility Considerations</a></DD>
</DL>
<!-- XXXXXXXXXXXXXXX START CONTENT: XXXXXXXXXXXXXXXXXXXX -->
<h3><A NAME="Introduction"></A>Introduction</h3>
<P>A major shortcoming of removable media devices on PC platforms is their inability to report to the host when the user attempts to eject the medium. Currently most removable media devices just eject the medium when the user presses the Eject button, and potentially any data the operating system has not saved to the device is lost. Various volume tracking and locking schemes reduce this risk, but do not eliminate it. Ideally, devices will have a means of communicating to the host that the user wants to eject the medium or has inserted a new medium.</P>
<P>This specification defines a protocol for providing this function for SCSI ATA and ATAPI devices. The support is enabled using a new SCSI command, ENABLE MEDIA STATUS, and the media status is retrieved using a new SCSI ATA command, GET MEDIA STATUS. </P>
<P>Because it is difficult for a SCSI target to asynchronously interrupt the host due to lack of industry support for Asynchronous Event Notification, the GET MEDIA STATUS command is not completed by the target until a media status change occurs. If tagged command queuing is not supported by the target and/or the host, a means of polling the target for status changes is also specified.
Note that in some controllers the unused words in the ID Drive data are returned as 0FFFFh. Thus it may be better if the Status Notification support was returned as a 2 bit field, where 00b, 11b are both defined as drive not supporting Status notification.</P>
<h3><A NAME="Enabling"></A>Enabling and Disabling Media Status Notification Support</h3>
<P>To maintain compatibility with existing BIOS implementations and operating systems, the target must assume that the host does shall not enableimplement Media Status Notification support until the ENABLE MEDIA STATUS command is issued by the host, as described in this section.</P>
<P>When the host enables the support using the ENABLE MEDIA STATUS command, the target shallmust respond as described in this specification. When the host disables this featuresupport, the target must default to normal operating modes. A SCSI bus reset, bus device reset or power on condition must also cause the target to return to normal operating modes.</P>
<P><b>ENABLE MEDIA STATUS Command</b></P>
<P>The ENABLE MEDIA STATUS command requests that the SCSI Target enable or disable Media Status Notification. If Media Status Notification is not supported, the target shall return CHECK CONDITION (Sense Key 05 ILLEGAL REQUEST, Sense Code 24 INVALID FIELD IN COMMAND PACKET).
</P>
<P>
<img src="scsienbl.gif" width=573 height=260 border=0></P>
<P>An Enable bit of one indicates that the target shall enable Media Status Notification. If the target currently has Media Status Notification enabled, the target shall return CHECK CONDITION (Sense Key 05 ILLEGAL REQUEST, Sense Code 4E OVERLAPPED COMMANDS ATTEMPTED).</P>
<P>An Enable bit of zero indicates that the target shall disable Media Status Notification.</P>
<h3><A NAME="Returning"></A>Returning Media Status</h3>
<P>The media status information is returned when the host issues the GET MEDIA STATUS command described below.</P>
<P><b>GET MEDIA STATUS Command</b></P>
<P>The ENABLE MEDIA STATUS command requests that the SCSI Target report media status changes. If Media Status Notification is not supported or not enabled, the target shall return CHECK CONDITION (Sense Key 05 ILLEGAL REQUEST, Sense Code 24 INVALID FILED IN COMMAND PACKET).</P>
<P>
<img src="scsigetm.gif" width=572 height=260 border=0></P>
<P>This command has two modes of operation. If the Immed bit is set to one, and if the state of the target is normal (that is, medium not inserted, Eject button not pushed), the GET MEDIA STATUS command shall return good status. If the state of the target has changed, a CHECK CONDITION command shall be returned, and the subsequent REQUEST SENSE command shall return the appropriate keys as defined in the Reporting Media Status Changes section below.</P>
<P>If the Immed bit is set to zero (and the target supports tagged command queuing) and if the state of the target is normal (that is, medium in the target, medium not changed, Eject button not pushed), the GET MEDIA STATUS command shall be queued by the target until the status of the medium changes, or some error condition occurs. If the state of the target has changed, a CHECK CONDITION command shall be returned, and the subsequent REQUEST SENSE command shall return the appropriate keys as defined in the Reporting Media Status Changes section below.</P>
<P>If the Immed bit is set to zero and the target DOES NOT support tagged command queuing, the target shall return CHECK CONDITION (Sense Key 05 ILLEGAL REQUEST, Sense Code 24 INVALID FIELD IN COMMAND PACKET).</P>
<h3><A NAME="Reporting"></A>Reporting Media Status Changes</h3>
<P>When a media status change has been detected, the GET MEDIA STATUS command shall return CHECK CONDITION. The target shall return the following sense data:</P>
<P>Sense Key 06 (UNIT ATTENTION)</P>
<P>Sense Code E0 (MEDIA STATUS CHANGE)</P>
<P>Additional Sense Code Qualifier:</P>
<P><b>00 - EJREQ </b></P>
<P>This Qualifier indicates that the user has attempted to eject the medium. Usually this Qualifier will be set when the user presses the Eject button on the target. If theThe target is capable of preventing removal of the media, the target shallmust not allow the medium to be ejected until an EJECT command is received from the host. This Qualifier shallmust not be set again in response to the GET MEDIA STATUS command until the user subsequently releases the button and presses it again.</P>
<P><b>01 - NEWMED</b></P>
<P>This Qualifier indicates that a medium has been newly inserted in the target. The Qualifier must not be set for more than one invocation of the GET MEDIA STATUS command, until the user removes or reinserts the medium. In other words, when the user inserts a new medium in the target, and a GET MEDIA STATUS command is issued, the target will set this Qualifier. The next GET MEDIA STATUS command must not result in this Qualifier being set again unless the medium has been removed and reinserted.</P>
<P>All other Qualifiers are reserved.</P>
<h3><A NAME="SCSI"></A>SCSI Compatibility Considerations</h3>
<P>SCSI commands must be processed exactly the same as they would be if Media Status Notification was not enabled. When the GET MEDIA STATUS command is received by the SCSI target, the status changed error codes must be reported as described in "Returning Media Status" earlier in this specification. However, the state of the bits must not be cleared by any other SCSI command. The insertion of a new medium must be reported independently with both the GET MEDIA STATUS and other SCSI commands. For example, if the user inserts a new medium and the target is accessed with an SCSI command, the CHECK CONDITION with UNIT ATTENTION must be reported, but the target must also report the NEMED error when it receives the next GET MEDIA STATUS command. The behavior must be the same if, after the medium is inserted, the GET MEDIA STATUS command is received before the next SCSI command.</P>
<P>When the user presses the Eject button on the target, the SCSI commands must not be affected, but the EJREQ status must be reported when the first GET MEDIA STATUS command is received after the button is pressed, (it is reported only once after each button press). The SCSI target must continue to operate as normal. If the host determines that it is safe to eject the medium, an SCSI EJECT command shall be issued to the target by the host, at which time the target shall eject the medium.</P>
<P><TABLE WIDTH=78% BORDER=1 CELLPADDING=5 CELLSPACING=0>
<TR VALIGN=TOP BGCOLOR="#80AADD">
<TD colspan=3><FONT FACE="Arial" SIZE=2><B>Revision Record</B></FONT></TD></TR>
<TR VALIGN=TOP>
<TD><FONT FACE="Arial" SIZE=2><b>Edition</b></FONT></TD>
<TD><FONT FACE="Arial" SIZE=2>Date Published</FONT></TD>
<TD><FONT FACE="Arial" SIZE=2>Revised Comments</FONT></TD></TR>
<TR VALIGN=TOP>
<TD><FONT FACE="Arial" SIZE=2>0.1</FONT></TD>
<TD><FONT FACE="Arial" SIZE=2>March 1996</FONT></TD>
<TD><FONT FACE="Arial" SIZE=2>First Draft Version</FONT></TD></TR>
</TABLE></P>
<P>Send comments to <A HREF="mailto:billpa@microsoft.com">billpa@microsoft.com</A>.</P>
<!-- XXXXXXXXXXXXXXXX END CONTENT XXXXXXXXXXXXXXXXXXXXXX -->
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<TABLE CELLPADDING=0 CELLSPACING=0 WIDTH=92% BORDER=0>
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<q class=date>File Date: July 7, 1998<br>
<!--COPYRIGHT STATEMENT--><A STYLE="color:#001144" STYLE="text-decoration:underline;" HREF="/misc/cpyright.htm">&copy; 1999 Microsoft Corporation. All rights reserved. Terms of Use.</A></q><BR></FONT>
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From marcj@nando.net Wed Mar 1 17:51:03 1995
From: marcj@nando.net (MarcJ)
Newsgroups: comp.os.msdos.programmer
Subject: CD-ROM FAQ
Date: 19 Feb 1995 23:18:50 -0500
Organization: NandO -- The News & Observer online service
NNTP-Posting-Host: parsifal.nando.net
In recognition of a number of questions I've seen recently asking
questions on programming CD-ROMs...
CD-ROM programming FAQ Version 1.00
Copyright (C) 1995 by Marcus W. Johnson. All rights reserved. This
article is not in the public domain, but it may be redistributed so
long as this notice, the acknowledgments, and the information on
obtaining the latest copy of this list are retained and no fee is
charged. The code fragments may be used freely; credit would be
polite.
------- Table of Contents --------------------------------------------
Section 0 - Availability
0.01. How can I get the latest copy of this FAQ?
Section 1 - MSCDEX Status
1.01. How do I know if MSCDEX is installed?
1.02. How do I determine the MSCDEX version?
Section 2 - CD-ROM Existence
2.01. How many CD-ROMs are present?
2.02. Which drives are CD-ROMs?
2.03. How do I get the name of the CD-ROM device driver?
Section 3 - Drive Interface
3.01. How do I open the door?
3.02. How do I close the door?
3.03. How do I unlock the door?
3.04. How do I lock the door?
3.05. How do I reset the drive?
3.06. How do I get drive status?
Section 4 - Drive Capacity
4.01. What sector size is supported?
4.02. How many sectors are on the disk?
4.03. How much data is on the disk?
Section 5 - Volume Table of Contents
5.01. How do I get the abstract file name?
5.02. How do I get the bibliography file name?
5.03. How do I get the copyright file name?
5.04. How do I read the Volume Table of Contents (VTOC)?
Section 6 - Audio
6.01. How do I find out how many tracks are on a CD?
6.02. What are Red Book and HSG formats?
6.03. How can I determine where a particular track starts?
6.04. How do I play audio?
6.05. How do I pause audio playback?
6.06. How do I resume audio playback?
======================================================================
Section 0 - Administration
----------------------------------------------------------------------
0.01. How can I get the latest copy of this FAQ?
The FAQ is published monthly in comp.os.msdos.programming and
alt.msdos.programmer.
----------------------------------------------------------------------
0.02. Where did this information come from?
Ralf Brown's interrupt list
"MS-DOS Extensions", by Ray Duncan, Microsoft Press
My personal research for "PC-Programmer's Guide to Low-Level
Functions and Interrupts", Sams
The mention of particular books or programs must not be construed
to reflect unfavorably on any that are not mentioned.
----------------------------------------------------------------------
0.03. How accurate is this information?
I have personally tested the code fragments in this FAQ, and
they appear to work as advertised, but there is no warranty on
the code or on the techniques described in this article.
As testing may not have been perfect, and machines and
configurations vary, it is possible that the fragments will not
work for you.
Please send corrections to marcj@nando.net.
======================================================================
Section 1 - MSCDEX Status
======================================================================
1.01. How do I know if MSCDEX is installed?
Call the MSCDEX installation check function. Here's code that
performs the check:
mov AX,0DADAH
push AX
mov AX,01100H
int 2FH
pop BX
cmp BX,0ADADH
jne not_installed
cmp AL,0FFH
jne not_installed
;
; MSCDEX is installed
;
----------------------------------------------------------------------
1.02. How do I determine the MSCDEX version?
Call the MSCDEX version check function. Here's code that gets
the version:
mov AX,150CH
int 2FH
;
; BH holds the major version
; BL holds the minor version
; Prior to MSCDEX version 2.0, the version returned is 0.0 (BX =
; 0)
;
======================================================================
Section 2 - CD-ROM Existence
======================================================================
2.01. How many CD-ROMs are present?
Ask MSCDEX. Here's code that gives the count of CD-ROMs
installed and the drive letter of the first one:
mov AX,1500H
xor BX,BX
int 2FH
;
; BX will hold the number of CD-ROMs
; CL will hold the first CD-ROM's drive; 0 = A:, 1 = B:, and so
; on
;
A problem with this method, BTW, is that it conflicts with DOS
4.0's GRAPHICS.COM.
----------------------------------------------------------------------
2.02. Which drives are CD-ROMs?
There are two ways to find out. Both ways require MSCDEX version
2 (see question 1.02, How do I determine the MSCDEX version?).
The first way gives a list of all CD-ROM drives; the second
verifies whether a specific drive is a CD-ROM.
Method 1: (get list of CD-ROMs)
This method requires a block of memory; the size, in bytes, must
be at least the number of drives returned by function 1500H (see
question 2.01, How many CD-ROMs are present?).
mov AX,150DH
les BX,LetterArray
int 2FH
;
; each byte in LetterArray will contain a drive value (0 = A:, 1
; = B:, etc.)
;
Method 2: (is a specified drive a CD-ROM?)
mov AX,150BH
mov CX,Drive ; 0 = A:, 1 = B:, and so on
int 2FH
or AX,AX
jz not_cd_rom
cmp BX,0ADADH
jne not_cd_rom
;
; the drive is a CD-ROM
;
----------------------------------------------------------------------
2.03. How do I get the name of the CD-ROM device driver?
First, you need to know how many CD-ROMs you have (see question
2.01, How many CD-ROMs are present?). You need a block of memory
whose size, in bytes, is 5 times the number of CD-ROMs present.
This code will fill that array:
mov AX,1501H
les BX,DriverArray
int 2FH
Each 5-byte element in the array consists of the drive's subunit
number (a CD-ROM device driver may support several drives as
subunits), followed by the address of the drive's device driver.
The filename is 10 bytes into the device driver. The filename is
at most 8 bytes long, and if less than 8 bytes, is terminated by
a space (20H).
======================================================================
Section 3 - Drive Interface
======================================================================
3.01. How do I open the door?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a one byte block of
memory. Call DOS IOCTL function 4403H, as shown here:
mov BX,FileHandle
mov Command,0
lds DX,Command
mov CX,1
mov AX,4403H
int 21H
jc error
cmp AX,1
jne write_error
;
; door should be open
;
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
----------------------------------------------------------------------
3.02. How do I close the door?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a one byte block of
memory. Call DOS IOCTL function 4403H, as shown here:
mov BX,FileHandle
mov Command,5
lds DX,Command
mov CX,1
mov AX,4403H
int 21H
jc error
cmp AX,1
jne write_error
;
; door should be closed
;
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
The drive should be reset after closing the door before
accessing the drive (see question 3.05, How do I reset the
drive?).
----------------------------------------------------------------------
3.03. How do I unlock the door?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a two-byte block of
memory. Call DOS IOCTL function 4403H, as shown here:
mov BX,FileHandle
mov Command,1
mov Command+1,0
lds DX,Command
mov CX,2
mov AX,4403H
int 21H
jc error
cmp AX,2
jne write_error
;
; door should be unlocked
;
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
The drive should be reset after unlocking the door before
accessing the drive (see question 3.05, How do I reset the
drive?).
----------------------------------------------------------------------
3.04. How do I lock the door?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a two-byte block of
memory. Call DOS IOCTL function 4403H, as shown here:
mov BX,FileHandle
mov Command,1
mov Command+1,1
lds DX,Command
mov CX,2
mov AX,4403H
int 21H
jc error
cmp AX,2
jne write_error
;
; door should be locked
;
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
The drive should be reset after locking the door before
accessing the drive (see question 3.05, How do I reset the
drive?).
----------------------------------------------------------------------
3.05. How do I reset the drive?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a one-byte block of
memory. Call DOS IOCTL function 4403H, as shown here:
mov BX,FileHandle
mov Command,2
lds DX,Command
mov CX,1
mov AX,4403H
int 21H
jc error
cmp AX,1
jne write_error
;
; drive should be reset
;
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
----------------------------------------------------------------------
3.06. How do I get drive status?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a five-byte block of
memory. Call DOS IOCTL function 4402H, as shown here:
mov BX,FileHandle
mov Command,6
lds DX,Command
mov CX,5
mov AX,4402H
int 21H
jc error
cmp AX,5
jne read_error
;
; The word at offset 1 of the five-byte block of memory contains
; status
; bit 10 is set if audio is playing
; bit 9 is set if Red Book and HSG addressing are both
; supported
; bit 8 is set if audio channel control is supported
; bit 7 is set if prefetch requests are supported
; bit 5 is set if interleaving is supported
; bit 4 is set if audio/video track playback is supported
; bit 3 is set if the CD-ROM is writable
; bit 2 is set if raw and cooked read is supported
; bit 1 is set if the door is unlocked
; bit 0 is set if the door is open
;
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
The drive should be reset after checking drive status before
accessing the drive (see question 3.05, How do I reset the
drive?).
======================================================================
Section 4 - Drive Capacity
======================================================================
4.01. What sector size is supported?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a four-byte block of
memory. Call DOS IOCTL function 4402H, as shown here:
mov BX,FileHandle
mov Command,7
lds DX,Command
mov CX,4
mov AX,4402H
int 21H
jc error
cmp AX,4
jne read_error
;
; The byte at offset 1 of the four-byte block of memory contains
; raw/cooked status (0 = cooked, 1 = raw)
; The word at offset 2 of the four-byte block of memory contains
; the sector size
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
The drive should be reset after getting the sector size before
accessing the drive (see question 3.05, How do I reset the
drive?).
----------------------------------------------------------------------
4.02. How many sectors are on the disk?
First, you need the name of the device driver (see question 2.03,
How do I get the name of the CD-ROM device driver?). Open the
file for read/write and obtain the file handle (DOS function 3DH
will suffice).
Once you have the file handle, you need a five-byte block of
memory. Call DOS IOCTL function 4402H, as shown here:
mov BX,FileHandle
mov Command,8
lds DX,Command
mov CX,5
mov AX,4402H
int 21H
jc error
cmp AX,5
jne read_error
;
; The dword at offset 1 of the five-byte block of memory
; contains the number of sectors
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
The drive should be reset after getting the number of sectors
before accessing the drive (see question 3.05, How do I reset
the drive?).
----------------------------------------------------------------------
4.03. How much data is on the disk?
See question 4.01, What sector size is supported?, and question
4.02, How many sectors are on the disk?. Take the product of the
two values returned. The conventional DOS functions don't work
reliably.
======================================================================
Section 5 - Volume Table of Contents
======================================================================
5.01. How do I get the abstract file name?
You need a 38-byte block of memory to hold the abstract file
name. This code will fill that block:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov AX,1503H
int 2FH
jc error
;
; buffer is filled with the abstract file name.
;
The file name is nul-terminated.
The drive should be reset after getting the abstract file name
before accessing the drive (see question 3.05, How do I reset
the drive?).
----------------------------------------------------------------------
5.02. How do I get the bibliography file name?
You need a 38-byte block of memory to hold the bibliography file
name. This code will fill that block:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov AX,1504H
int 2FH
jc error
;
; buffer is filled with the bibliography file name.
;
The file name is nul-terminated.
The drive should be reset after getting the bibliography file
name before accessing the drive (see question 3.05, How do I
reset the drive?).
----------------------------------------------------------------------
5.03. How do I get the copyright file name?
You need a 38-byte block of memory to hold the copyright file
name. This code will fill that block:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov AX,1502H
int 2FH
jc error
;
; buffer is filled with the copyright file name.
;
The file name is nul-terminated.
The drive should be reset after getting the copyright file name
before accessing the drive (see question 3.05, How do I reset
the drive?).
----------------------------------------------------------------------
5.04. How do I read the Volume Table of Contents (VTOC)?
The VTOC is read in 2048-byte blocks. This code fills a VTOC
block:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov DX,BlockNumber ; 0 for the first block
mov AX,1505H
int 2FH
jc error
;
; block is filled
;
; AX contains the descriptor type for this block:
; 0001H = standard volume descriptor
; 00FFH = volume descriptor terminator
;
On error, AX will hold an error value: 000FH (invalid drive) or
0015H (drive not ready).
======================================================================
Section 6 - Audio
======================================================================
6.01. How do I find out how many tracks are on a CD?
First, you need the name of the device driver (see question
2.03, How do I get the name of the CD-ROM device driver?). Open
the file for read/write and obtain the file handle (DOS function
3DH will suffice).
Once you have the file handle, you need a seven-byte block of
memory. Call DOS IOCTL function 4402H, as shown here:
mov BX,FileHandle
mov Command,0AH
lds DX,Command
mov CX,7
mov AX,4402H
int 21H
jc error
cmp AX,7
jne read_error
;
; The byte at offset 1 of the seven-byte block of memory is the
; number of the first track
; The byte at offset 2 of the seven-byte block of memory is the
; number of the last track
; The dword at offset 4 of the seven-byte block of memory is the
; start address of the first track in Red Book format
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
----------------------------------------------------------------------
6.02. What are Red Book and HSG formats?
Both are ways of encoding frame information. An audio frame is
1/75 second of audio. HSG encodes frame information into a
double word: minute multiplied by 4500, plus second multiplied
by 75, plus frame, minus 150. Red Book encodes frame information
into a four-byte data structure:
Byte 0: frame number
Byte 1: second
Byte 2: minute
Byte 3: unused
----------------------------------------------------------------------
6.03. How can I determine where a particular track starts?
First, you need the name of the device driver (see question
2.03, How do I get the name of the CD-ROM device driver?). Open
the file for read/write and obtain the file handle (DOS function
3DH will suffice).
Once you have the file handle, you need an eight-byte block of
memory. Call DOS IOCTL function 4402H, as shown here:
mov BX,FileHandle
mov Command,0BH
mov Command+1,TrackNumber
lds DX,Command
mov CX,8
mov AX,4402H
int 21H
jc error
cmp AX,8
jne read_error
;
; The dword at offset 2 of the eight-byte block of memory is the
; start address of the specified track in Red Book format
; The word at offset 6 of the eight-byte block of memory is the
; track control information. Bits 15-12 are used:
; 0xxx: Two audio channels, no pre-emphasis, digital copy not
; permitted
; 1xxx: Two audio channels, with pre-emphasis, digital copy not
; permitted
; 2xxx: Two audio channels, no pre-emphasis, digital copy
; permitted
; 3xxx: Two audio channels, with pre-emphasis, digital copy
; permitted
; 4xxx: Data track, digital copy not permitted
; 6xxx: Data track, digital copy permitted
; 8xxx: Four audio channels, no pre-emphasis, digital copy not
; permitted
; 9xxx: Four audio channels, with pre-emphasis, digital copy not
; permitted
; Axxx: Four audio channels, no pre-emphasis, digital copy
; permitted
; Bxxx: Four audio channels, with pre-emphasis, digital copy
; permitted
On error (carry set), AX will hold an error code: 0001H (invalid
function), 0005H (access denied), 0006H (invalid handle), or
000DH (invalid data).
----------------------------------------------------------------------
6.04. How do I play audio?
For starters, you need MSCDEX Version 2.1 or greater (see
question 1.02, How do I determine the MSCDEX version?).
You also need the subunit number for the drive containing the
audio CD (see question 2.03, How do I get the name of the CD-ROM
device driver?)
You also need to know what frame you want to start with (see
question 6.03, How can I determine where a particular track
starts?), and how many frames you want to play.
Now, you need a 22-byte block of memory. Write 22 (16H) to the
first byte. Write the subunit number to the second byte. Write
84H to the third byte. Write 0 to the byte at offset 0DH (this
sets up HSG addressing). Convert the starting frame number to
HSG format and write the 4-byte result to the dword at offset
0EH. Finally, write the frame count to the dword at offset 12H.
To play the CD as instructed, execute this code:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov AX,1510H
int 2FH
;
; status is in the word at offset 3 of the buffer. Look for bit
; 8 set (done), and watch out for bit 15 set (error).
;
----------------------------------------------------------------------
6.05. How do I pause audio playback?
For starters, you need MSCDEX Version 2.1 or greater (see
question 1.02, How do I determine the MSCDEX version?).
You also need the subunit number for the drive containing the
audio CD (see question 2.03, How do I get the name of the CD-ROM
device driver?)
Now, you need a 13-byte block of memory. Write 13 (0DH) to the
first byte. Write the subunit number to the second byte. Write
85H to the third byte.
To pause the CD, execute this code:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov AX,1510H
int 2FH
;
; status is in the word at offset 3 of the buffer. Look for bit
; 8 set (done), and watch out for bit 15 set (error).
;
----------------------------------------------------------------------
6.06. How do I resume audio playback?
For starters, you need MSCDEX Version 2.1 or greater (see
question 1.02, How do I determine the MSCDEX version?).
You also need the subunit number for the drive containing the
audio CD (see question 2.03, How do I get the name of the CD-ROM
device driver?)
Now, you need a 13-byte block of memory. Write 13 (0DH) to the
first byte. Write the subunit number to the second byte. Write
88H to the third byte.
To resume, execute this code:
les BX,Buffer
mov CX,Drive ; must be in format 0 = A:, 1 = B:, etc.
mov AX,1510H
int 2FH
;
; status is in the word at offset 3 of the buffer. Look for bit
; 8 set (done), and watch out for bit 15 set (error).
;

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