[Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

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[Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by Battler »

First, check the date. If the date is before November 11th, 1991, then it's most likely 5.00, if it's dated November 11th, 1991, or later, it's most likely 5.00a.

Second, check IO.SYS and FORMAT.COM. This is what you need to look for:

IO.SYS:
- 5.00 has the sequence B4 30 at offset 0x0238, whereas 5.00a has the sequence 8C C8 at the same offset;
- 5.00 has the sequence FE FF at offset 0x023D, whereas 5.00a has the sequence 05 01 at the same offset.

FORMAT.COM:
- 5.00 has the sequence E8 1E 02 73;
- 5.00a has the sequence E8 4E 02 73 instead.

Note that this is only for PC and compatible versions. Non-PC-compatible versions (for PC-98, FM-Towns, etc.), are most likely not identifiable that way and most probably have a different set of versions anyway.
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Re: [Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by TheCollector1988 »

this would become handy to identify PC-compatible OEM versions of MS-DOS 5.00 (non-a) released after November 1991 :)

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Re: [Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by Battler »

And to identify if a non-English version is 5.00 or 5.00a, because they often don't have the same dates/times as the English ones so the byte checks are the most reliable way to distinguish them.
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Re: [Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by Battler »

Another difference, mentioned here: support.microsoft.com/KB/73322 . MS-DOS 5.00 has EMM386.EXE version 4.20, while MS-DOS 5.00a has EMM386.EXE version 4.33.
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Re: [Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by os2fan2 »

Also, all of the MS-DOS 5 fixes on the microsoft server update 5.00 to 5.00a. So that's where to look.

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Re: [Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by Battler »

MS-DOS 5.00 Russian (dated August 1991), and Dutch (06-24 edition, haven't verified the July edition yet) both have the MS-DOS 5.00a sequences in IO.SYS but the MS-DOS 5.00 sequence in FORMAT.COM and EMM386.EXE version 4.20. This places them somewhere between 5.00 and 5.00a.

Edit: The July edition of MS-DOS 5.00 Dutch has the same situation.
IO.SYS:
- 5.00 has the sequence B4 30 at offset 0x0238, whereas 5.00a has the sequence 8C C8 at the same offset;
- 5.00 has the sequence FE FF at offset 0x023D, whereas 5.00a has the sequence 05 01 at the same offset.
Edit #2: It seems the 720k non-upgrade version of MS-DOS 5.00 that I provided is literally the *ONLY* dos which has the sequence I labeled as 5.00 in IO.SYS, every other DOS copy, from at least 5.00 RC 10 all the way to 6.22 has the sequence I labeled as 5.00a. Considering this is a code sequence that initializes the stack segment, and the sequence I labeled as 5.00a produces code that makes much more sense (sets AX to CS, then SS to AX, then SP to 0105h), I conclude that that 720k version was most probably dumped from a bad floppy where those 4 bytes of IO.SYS were damaged, and that this sequence has nothing to do with whether the DOS is 5.00 or 5.00a, though I am still investigating on whether the unique sequence from that 720k version really doesn't appear in any other version of IO.SYS.

So the way to distinguish between MS-DOS 5.00 and 5.00a is the sequence in FORMAT.COM, and the version of EMM386 (4.20 in 5.00 and 4.33 in 5.00a).
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Re: [Guide] How to identify if MS-DOS 5.0 is 5.00 or 5.00a?

Post by Battler »

I have since found more differences between MS-DOS 5.00 and 5.00a:
- MS-DOS 5.00a has 8514.VID (DOSSHELL 8514/a driver) and PRINTFIX.COM, MS-DOS 5.00 does not;
- A few other files also differ, but I'vet to compare their contents and identify the differences.
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