🚀 go-pugleaf

>From:    Mike Ramey <mramey@u.washington.edu>
>Subject: RE: Dangerous bug in CHKDSK that comes with MS-DOS 5.0 (PC) (fwd)

>I called Microsoft and requested the updated version for my computer
>labs, even tho' we have not encountered the failure conditions yet.  I
>was told that in MS-DOS version 5.0a, the date on COMMAND.COM is
>11-11-91.

Just tried the VER /R trick after booting from a (relatively) old floppy
with IO.SYS, MS-DOS.SYS, and COMMAND.COM all dated 03-22-91 5:10a. Guess
what the report was:

MS-DOS Version 5.00
Revision A
DOS is in low memory

Further, COMP finds no difference between this COMMAND.COM and the one I
just expanded from a new set of distribution disks that is dated 11-11-91.

However, COMP *does* find a difference between the earlier CHKDSK.EXE and
the one dated 11-11-91, which has a three byte change (to make sure that
the CH value is cleared ?)

Assuming that this is causing the problem, DEBUG will find the string: 

 8b 4f 0f 8b f9 (MOV CX,[BX+0F] MOV DI,CX) at offset ds:263e in the "old" and
 8b 7f 0f 32 ed (MOV DI,[BX+0F] XOR CH,CH) is at the same offset in the "new"

CHKDSK.EXE. Both are 16,200 bytes long.

Sounds like there may be more than one revision A  (or why ver /r is
undocumented).

					Warmly,
						Padgett

Note: this was done without any advice/observations from Mircrosoft &
      only represents what I found in minimal testing. Caveat y'all.