71 lines
3.0 KiB
HTML
71 lines
3.0 KiB
HTML
<html><head>
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<title>HPFS: HPFS Volume Structure</title>
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</head>
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<body>
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<center>
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<h1>HPFS Volume Structure</h1>
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</center>
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HPFS volumes are a new partition type--type 7--and can exist on a fixed disk
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alongside of the several previously defined FAT partition types.
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IBM-compatible HPFS volumes use a sector size of 512 bytes and have a maximum
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size of 2199Gb (232 sectors).
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Although there is no particular reason why floppy disks can't be formatted
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as HPFS volumes Microsoft plans to stick with FAT file systems on floppy disks
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for the foreseeable future.
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(This ensures that users will be able to transport files easily between MS-DOS
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and OS/2 systems.)
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An HPFS volume has very few fixed structures (<a href="#fig1">Figure 1</a>).
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Sectors 0-15 of a volume (8Kb) are the Bootblock and contain a volume name,
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32-bit volume ID, and a disk bootstrap program. The bootstrap is relatively
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sophisticated (by MS-DOS standards) and can use the HPFS in a restricted
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mode to locate and read the operating system files wherever they might be found.
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Sectors 16 and 17 are known as the Super Block and the Spare Block respectively.
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The Super Block is only modified by disk maintenance utilities.
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It contains pointers to the free space bitmaps the bad block list the directory
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block band and the root directory.
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It also contains the date that the volume was last checked out and repaired
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with CHKDSK /F. The Spare Block contains various flags and pointers that
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will be discussed later it is modified although infrequently as the system
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executes. The remainder of the disk is divided into 8Mb bands.
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Each band has its own free space bitmap in which a bit represents each sector.
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A bit is 0 if the sector is in use and 1 if the sector is available.
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The bitmaps are located at the head or tail of a band so that two bitmaps are
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adjacent between alternate bands. This allows the maximum contiguous free space
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that can be allocated to a file to be 16Mb. One band located at or toward the
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seek center of the disk is called the directory block band and receives
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special treatment (more about this later). Note that the band size is a
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characteristic of the current implementation and may be changed in later
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versions of the file system.
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<p>
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<center>
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<a href="fig1.gif" name="fig1">
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<img src="fig1.gif" alt="[Fig. 1]" border=0></a>
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</center>
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<p>
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<b>FIGURE 1</b>.
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This figure shows the overall structure of an HPFS volume.
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The most important fixed objects in such a volume are the Bootblock the Super
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Block, and the Spare Block.
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The remainder of the volume is divided into 8Mb bands.
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There is a freespace bitmap for each band and the bitmaps are located between
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alternate bands consequently, the maximum contiguous space which can be
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allocated to a file is 16Mb.
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<p>
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<hr>
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< <a href="fat.html">[FAT File System]</a> |
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<a href="hpfs.html">[HPFS Home]</a> |
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<a href="fnodes.html">[Files and Fnodes]</a> >
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<hr>
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<font size=-1>
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Html'ed by <a href="http://www.seds.org/~spider/">Hartmut Frommert</a>
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</font>
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</body></html>
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