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1991-06-08
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Documentation for FIXFAT Copyright 1991, P. R. Fletcher _________________________ _______________________________
INTRODUCTION ____________
FIXFAT is part of the HDTEST package, and is distributed with the
Shareware and Registered versions of that software. The program and
documentation may only be used or copied under the conditions laid
down in the DOC files distributed with the package. The program allows
DOS's two on-disk copies of the FAT to be made to correspond, when
they have got "out of sync". This is required for HDCHEK and HDTEST to
run. FIXFAT is only intended to be used when something has happened to
corrupt or alter one copy of the FAT (usually because the second copy ___
was only partially updated when a disk write was immediately followed
by a reboot or use of the "big red switch"). The program cannot repair
the FAT if both copies have become corrupted, nor is it intended to be
a replacement for CHKDSK or the more complex disk repair utilities
that are supplied with (e.g.) the Norton and Mace Utilities (TM).
Users who have, and are comfortable with, the latter utilities will
probably find FIXFAT superfluous. It is intended to provide a simple,
limited, but fairly safe way for less experienced users to correct
minor FAT problems prior to running HDTEST.
FIXFAT is Copyright by Peter R. Fletcher, 1991. All rights are
reserved. It was largely written in C, compiled with the Microsoft C
compiler (V6.0A). A few low-level functions were written in assembly
language and assembled with the Microsoft MASM assembler (V6.0). The
program was linked with code from the Microsoft C function libraries
by means of the Microsoft LINK linker (V5.13). It consequently
contains material that is Copyright by Microsoft Corp, 1985-1990. This
material is used under the terms of a license from Microsoft Corp.
USING THE PROGRAM _________________
You should generally run CHKDSK before running FIXFAT, unless you have ______
some good reason to believe that the primary copy (and only the _____________
primary copy of the FAT on your disk (FAT 1) has been corrupted. If ____________
CHKDSK reports any problems other than "orphan clusters", you should,
if possible, also back up any irreplaceable files on the disk before
either using CHKDSK with its /F option or running FIXFAT. If both your
FATs have been damaged (e.g. by a defective program writing junk to
the FAT area), neither CHKDSK nor FIXFAT will be able to help you, and
your only hope is to use a disk repair utility such as those provided
with the Mace or Norton Utilities (TM).
The command line syntax for FIXFAT is:
FIXFAT dev[:]
"dev" is the single letter DOS device identifier for the device whose
FAT is to be fixed - the colon is optional. FIXFAT will first read and
compare the two copies of the FAT on the target disk. If they are
identical, this fact will be reported and the program will terminate.
If there are any discrepancies between the two copies of the FAT, the
program will examine them individually for evidence of corruption. If
FAT 1 appears valid, you will be prompted for permission to overwrite
FAT 2 with a copy of FAT 1. If FAT 1 appears invalid but FAT 2 appears __
Documentation for FIXFAT Copyright 1991, P. R. Fletcher _________________________ _______________________________
valid, you will similarly be prompted for permission to overwrite FAT
1 with a copy of FAT 2. If neither FAT appears valid, this will be
reported and the program will terminate. In determining whether a copy
of the FAT is valid, FIXFAT makes similar checks to those performed by
CHKDSK, except that "orphan clusters" (chains of clusters with no
corresponding directory entries) are not flagged as problems. The
occasional appearance of orphan clusters was rather common under
versions of DOS prior to 3.0, usually following a program abort, and
these are still not (usually) evidence of major trouble.
LIMITATIONS AND RESTRICTIONS ____________________________
FIXFAT uses the DOS disk interrupts (INT 25 and 26) to access the disk
- the program will not run on hardware/software combinations that do
not support the use of these interrupts (this is almost never a
problem). The program will, however, not run in the DOS compatibility ___
box under OS/2. FIXFAT requires an amount of free memory (over and
above that which it uses for its own code) that is equal to at least
four times the size of the FAT on the target device. For most devices,
512 kB should be more than enough, but a device whose size pushes DOS
4.0's limits may be more than the program can handle. For this version
of the program, a previous (undocumented) restriction on sector size
to the normal DOS value of 512 bytes has been lifted.
ADDITIONAL INFORMATION ______________________
Like all well-behaved programs (!), FIXFAT signals successful
completion by returning to DOS with the ERRORLEVEL variable set to
zero. Different small positive values are returned for various errors.
Comments, suggestions, etc. may be addressed to the author at:
1515 West Montgomery Avenue
Rosemont
PA 19010
U.S.A.
Please enclose a s.a.e. if you would like to receive a reply to a
question or a response to a comment.
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