Obscure DOS question

Eric Smith eric at brouhaha.com
Mon Mar 28 18:44:55 CST 2005

Tom wrote:
> If you fudge it somehow, chkdsk will
> say that it's broken and offer to fix it.

Wanna bet?

I "fudged it somehow" using the Linux mkdosfs utility.
Here's the output from Windows XP chkdsk:

The type of the file system is FAT.
Volume Serial Number is 4248-9A4E
Windows is verifying files and folders...
6 percent completed. ....
12 percent completed.
19 percent completed.
25 percent completed..
32 percent completed..
38 percent completed...
44 percent completed...
51 percent completed...
57 percent completed....
64 percent completed....
70 percent completed.....
76 percent completed.....
83 percent completed.....
89 percent completed......
96 percent completed......
File and folder verification is complete.
Windows has checked the file system and found no problems.

    1,432,064 bytes total disk space.
      346,112 bytes in 676 files.
    1,085,952 bytes available on disk.

          512 bytes in each allocation unit.
        2,797 total allocation units on disk.
        2,121 allocation units available on disk.

I suppose it's possible that earlier versions of MS-DOS chkdsk
could complain, but I doubt that they do.  The on-disk structures
are all correct according to Microsoft's published documentation
on the FAT file system format.

In the olden days (DOS 2.x), OEMs were *expected* to define new
disk geometries, etc., so it's not surprising that the code is
smart enough to use the parameters in the boot block, and follow
the FAT chain for the root directory, rather than actually having
a hard-coded constant.  It's just the format command that is
somewhat inflexible.


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