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LZ-DOS


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#1 wendy

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Posted 16 May 2011 - 11:41 AM

Having heard the rumour that the command.com might be a hacked version of some PC-DOS, i decided to look. I have a small collection of pc-dos, so i gave it a whirl.

1. LZ-DOS runs rexx scripts, just like pcdos.

2. The file dates on LZ-DOS is 11/9/2003, which is identical to the build date on pc-dos 7.10.0129. In my collection, the context for this build is Norton Ghost 8.00.

3. Command.com in LZ is 53834, against 53802 for pcdos. Adding some 32 bits to pcdos, we see a very close match between the two, to the point where the bulk of the file is a light string hack (gsar -s"PC DOS" -r"LZ-DOS" -o command.com), does most of the work.

#2 Nuno Brito

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Posted 16 May 2011 - 11:26 PM

Hi Wendy,

Can you detail where is this "LZ-DOS" being used?

Thanks.

#3 Wonko the Sane

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Posted 17 May 2011 - 07:02 AM

Can you detail where is this "LZ-DOS" being used?


Whenever you need a DOS and you don't have one.

LZ-DOS - which is generally reputed as being the "most compatible to MS-DOS DOS" around - and actually (probably) it is a rip-off of actual MS-DOS (plus, as seen by Wendy :thumbup: a rip-off of PC-DOS) is not really "news":
http://reboot.pro/5497/
http://reboot.pro/5497/page__st__8
the fact that command.com is possibly coming from PC-DOS, is the actual "news". :cheers:

:ph34r:
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#4 wendy

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Posted 17 May 2011 - 08:45 AM

I have a copy of pc-dos command.com from build 1.29. It's no great trouble to do the comparisons.

Well, if you insert 32 bytes into the beginning of 1.29 command.com, and run the lot through tfc, you will indeed discover that the bulk of the differences between 1.29 command.com and lz-dos command.com lies entirely in PC DOS -> LZ-DOS, and a few copyright strings. There is a single change of byte elsewhere in the file (05 -> 06 or something).

However, when i ran the diffs between pcdos 5.02, and my rebuild of it, there were exactly four bytes different, so i suspect that this extranious byte is one of the known hacks. The bit about 'you should not try to compress command.com' is written over where the bldlevel string is in 1.29

The displacement of 32 bytes at the beginning has been discussed elsewhere, though not as a difference between 53834-53802. The displacement seems that the LZ dos has a different resident size to PC-DOS.

You can always go looking for a string REXX.EXE (which is in pc-dos 7.x, in OS/2 for PPC (a kind of 6.3), and no other dos.

Now we just have to figure out what IO.SYS means.

#5 Nuno Brito

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Posted 17 May 2011 - 05:25 PM

Ok then. Thank you Wonko for explaining, now I understand better the importance of this discovery.

:dubbio:

#6 TomE

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Posted 19 May 2011 - 04:47 PM

see also http://www.bttr-soft...der=last_answer
'LZ-DOS 7.1 *IS* MSDOS 7.1'
where I argue that LZDOS kernel is the MSDOS 7.1 (Win95) kernel

#7 tikbalang

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Posted 19 May 2011 - 06:31 PM

LZ's io.sys was compressed with apack.com.

#8 Nuno Brito

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Posted 19 May 2011 - 07:07 PM

Thanks for shedding more light on this matter.




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