[comp.sys.ibm.pc] DOS 4.0 filesystem

hinton@netcom.UUCP (Greg Hinton) (10/21/89)

The structure of the MS-DOS filesystem through version 3.30 is very well
documented in such books as _The MS-DOS Encyclopedia_, etc.
But so far I haven't been able to find a single thing detailing
the structure of the so-called "Bigfoot" filesystem used in versions
3.31 and 4.0.  None of the third-party books that claim to be updated
for version 4.0 have anything.  A call to Microsoft technical assistance
got nowhere.

Can anyone out there lead me to this information?  It must be documented
somewhere.  Any assistance is greatly appreciated.

Thank you.
-- 
Greg Hinton
DOMAIN: hinton@netcom.uucp
UUCP: uunet!apple!netcom!hinton

chasm@attctc.Dallas.TX.US (Charles Marslett) (10/23/89)

In article <3284@netcom.UUCP>, hinton@netcom.UUCP (Greg Hinton) writes:
> The structure of the MS-DOS filesystem through version 3.30 is very well
> documented in such books as _The MS-DOS Encyclopedia_, etc.
> But so far I haven't been able to find a single thing detailing
> the structure of the so-called "Bigfoot" filesystem used in versions
> 3.31 and 4.0.  None of the third-party books that claim to be updated
> for version 4.0 have anything.  A call to Microsoft technical assistance
> got nowhere.
> 
> Can anyone out there lead me to this information?  It must be documented
> somewhere.  Any assistance is greatly appreciated.

The 4.0 file system is really just like the old 3.0 (16-bit FAT) file system:
but since it now allows the product of the number of clusters and the size
of a cluster (in sectors) to be greater than 65535, it allows the disk
partition to exceed 32 MB (with a 512-byte sector size).

The real impact was that the INT 25h and INT 26h (I believe, anyway, the
read sector and write sector interrupt calls) now are passed the sector
number in memory (or on the stack, I can't remember for sure).  This allows
DOS to access sectors past 65535.  Of course, the FAT can be bigger (up to
65537 words or 129(?) sectors).

There are also some minor differences (I think they are minor, anyway) in the
structure of the partition tables, but you normally can ignore these.

> Thank you.
> -- 
> Greg Hinton

You're very welcome (and I hope I have helped, in fact),

Charles

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