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<TITLE>Int 13/AH=08h
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Int 13/AH=08h - DISK - GET DRIVE PARAMETERS (PC,XT286,CONV,PS,ESDI,SCSI) -
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AH = 08h
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DL = drive (bit 7 set for hard disk)
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ES:DI = 0000h:0000h to guard against BIOS bugs
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Return: CF set on error
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AH = status (07h) (see #00234)
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CF clear if successful
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AH = 00h
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AL = 00h on at least some BIOSes
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BL = drive type (AT/PS2 floppies only) (see #00242)
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CH = low eight bits of maximum cylinder number
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<h2>Int 13/AH=08h
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<p><img src="rbline.gif" tppabs="http://graphics.ctyme.com/gif/rbline.gif" width="100%" alt="------"><p>
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<h3><font color=#C00040>DISK - GET DRIVE PARAMETERS (PC,XT286,CONV,PS,ESDI,SCSI)</font></h3>
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<PRE>
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AH = 08h
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DL = drive (bit 7 set for hard disk)
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ES:DI = 0000h:0000h to guard against BIOS bugs<br>
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<p><b>Return:</b><br>CF set on error
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AH = status (07h) <a href="rb-0606.htm#Table234" tppabs="http://www.ctyme.com/intr/rb-0606.htm#Table234">(see #00234)</a>
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CF clear if successful
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AH = 00h
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AL = 00h on at least some BIOSes
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BL = drive type (AT/PS2 floppies only) <a href="rb-0621.htm#Table242" tppabs="http://www.ctyme.com/intr/rb-0621.htm#Table242">(see #00242)</a>
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CH = low eight bits of maximum cylinder number
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CL = maximum sector number (bits 5-0)
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high two bits of maximum cylinder number (bits 7-6)
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DH = maximum head number
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DL = number of drives
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ES:DI -> drive parameter table (floppies only)
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</PRE>
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<p><b>Notes:</b>
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May return successful even though specified drive is greater than the
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number of attached drives of that type (floppy/hard); check DL to
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ensure validity.
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For systems predating the IBM AT, this call is only valid for hard
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disks, as it is implemented by the hard disk BIOS rather than the
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ROM BIOS.
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The IBM ROM-BIOS returns the total number of hard disks attached
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to the system regardless of whether DL >= 80h on entry..
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Toshiba laptops with HardRAM return DL=02h when called with DL=80h,
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but fail on DL=81h. The BIOS data at 40h:75h correctly reports 01h..
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May indicate only two drives present even if more are attached; to
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ensure a correct count, one can use AH=15h to scan through possible
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drives.
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Reportedly some Compaq BIOSes with more than one hard disk controller
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return only the number of drives DL attached to the corresponding
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controller as specified by the DL value on entry. However, on
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Compaq machines with "COMPAQ" signature at F000h:FFEAh,
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MS-DOS/PC DOS IO.SYS/IBMBIO.COM call INT 15/AX=E400h and
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INT 15/AX=E480h to enable Compaq "mode 2" before retrieving the count
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of hard disks installed in the system (DL) from this function..
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The maximum cylinder number reported in CX is usually two less than
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the total cylinder count reported in the fixed disk parameter table
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(see INT 41h,INT 46h) because early hard disks used the last cylinder
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for testing purposes; however, on some Zenith machines, the maximum
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cylinder number reportedly is three less than the count in the fixed
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disk parameter table..
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For BIOSes which reserve the last cylinder for testing purposes, the
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cylinder count is automatically decremented.
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On PS/1s with IBM ROM DOS 4, nonexistent drives return CF clear,
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BX=CX=0000h, and ES:DI = 0000h:0000h.
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Machines with lost CMOS memory may return invalid data for floppy
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drives. In this situation CF is cleared, but AX,BX,CX,DX,DH,DI,
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and ES contain only 0. At least under some circumstances, MS-DOS/
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PC DOS IO.SYS/IBMBIO.COM just assumes a 360 KB floppy if it sees
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CH to be zero for a floppy..
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The PC-Tools PCFORMAT program requires that AL=00h before it will
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proceed with the formatting.
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If this function fails, an alternative way to retrieve the number
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of floppy drives installed in the system is to call INT 11h..
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In fact, the MS-DOS/PC-DOS IO.SYS/IBMBIO.COM attempts to get the
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number of floppy drives installed from INT 13/AH=08h, when INT 11h
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AX bit 0 indicates there are no floppy drives installed. In addition
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to testing the CF flag, it only trusts the result when the number of
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sectors (CL preset to zero) is non-zero after the call.
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<p><b>BUGS:</b>
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Several different Compaq BIOSes incorrectly report high-numbered
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drives (such as 90h, B0h, D0h, and F0h) as present, giving them the
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same geometry as drive 80h; as a workaround, scan through disk
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numbers, stopping as soon as the number of valid drives encountered
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equals the value in 0040h:0075h.
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A bug in Leading Edge 8088 BIOS 3.10 causes the DI,SI,BP,DS, and ES
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registers to be destroyed.
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Some Toshiba BIOSes (at least before 1995, maybe some laptops???
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with 1.44 MB floppies) have a bug where they do not set the ES:DI
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vector even for floppy drives. Hence these registers should be
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preset with zero before the call and checked to be non-zero on
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return before using them. Also it seems these BIOSes can return
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wrong info in BL and CX, as S/DOS 1.0 can be configured to preset
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these registers as for an 1.44 MB floppy..
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The PS/2 Model 30 fails to reset the bus after INT 13/AH=08h and
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INT 13/AH=15h. A workaround is to monitor for these functions
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and perform a transparent INT 13/AH=01h status read afterwards.
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This will reset the bus. The MS-DOS 6.0 IO.SYS takes care of
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this by installing a special INT 13h interceptor for this purpose..
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AD-DOS may leave interrupts disabled on return from this function..
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Some Microsoft software explicitly sets STI after return.
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<p><b>See Also:</b>
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<a href="rb-0616.htm" tppabs="http://www.ctyme.com/intr/rb-0616.htm">AH=06h"Adaptec"</a> - <a href="rb-0637.htm" tppabs="http://www.ctyme.com/intr/rb-0637.htm">AH=13h"SyQuest"</a> - <a href="rb-0715.htm" tppabs="http://www.ctyme.com/intr/rb-0715.htm">AH=48h</a> - <a href="rb-0639.htm" tppabs="http://www.ctyme.com/intr/rb-0639.htm">AH
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<p><b>See Also:</b>
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<a href="rb-6135.htm" tppabs="http://www.ctyme.com/intr/rb-6135.htm">INT 41"HARD DISK 0"</a>
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<PRE>
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<p>
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<a name=table242></a>
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(Table 00242)
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Values for diskette drive type:
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01h 360K
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02h 1.2M
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03h 720K
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04h 1.44M
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05h ??? (reportedly an obscure drive type shipped on some IBM machines).
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2.88M on some machines (at least AMI 486 BIOS)
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06h 2.88M
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10h ATAPI Removable Media Device
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</PRE>
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<p>
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<b>Category: <a href="cat-003.htm" tppabs="http://www.ctyme.com/intr/cat-003.htm">
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Bios</a>
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- <a href="int-13.htm" tppabs="http://www.ctyme.com/intr/int-13.htm">
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Int 13h</a>
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