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From: PCOEN@DRUNIVAC.BITNET (Paul R. Coen)
Newsgroups: comp.virus
Subject: Re: Zenith OEM MS-DOS (PC)
Message-ID: <0010.9104081309.AA03138@ubu.cert.sei.cmu.edu>
Date: 5 Apr 91 19:02:00 GMT
Sender: Virus Discussion List <VIRUS-L@LEHIIBM1>
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Approved: krvw@sei.cmu.edu


        The Zenith versions of MS-DOS are a little different than the
"standard" MS- and PC-DOS.

On earlier versions (3.2 and 3.21 -- I haven't used any earlier ones),
the current time and date was occasionally saved to the boot sector.
That's how the disks "remembered" the approximate time of last use on
boot-up (assuming no real-time-clock).

This caused the boot sector checksum to change.  Frequently.  It
really freaked me out the first time I noticed it :-).

Zenith DOS 3.3+ (equivalent to Compaq 3.31) does away with this.  I
guess they assume that everyone has real-time clocks in their pc's
these days.  All of the new Zeniths are shipped with them, anyway.  By
the way, different releases of 3.3+ leave very different amounts of
free memory (some use up to 20K of RAM more than others).

I'd assume Zenith 4.01 acts the same way as 3.3+.  I have this
aversion to to DOS 4.01, so I haven't tested it extensivly.
                            ------------
    Brought to you from Drew University, land of the 2,000+ Zeniths.
          Paul Coen -- Drew University Academic Computer Center
            pcoen@drunivac.bitnet     pcoen@drunivac.drew.edu