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From: mcastle@mcs213f.cs.umr.edu (Mike Castle (Nexus))
Newsgroups: comp.os.msdos.programmer
Subject: Re: Executrix info wanted
Message-ID: <1911@umriscc.isc.umr.edu>
Date: 10 Jan 91 00:20:08 GMT
References: <1991Jan9.075800.1019@ducvax.auburn.edu>
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Organization: University of Missouri - Rolla
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In article <1991Jan9.075800.1019@ducvax.auburn.edu> swanger@ducvax.auburn.edu writes:
>I recently received an ad from Knowledge Dynamics Corporation about a product
>of theirs named Executrix.  The following is an excerpt from the ad:
>
>Executrix supposedly compresses .EXE files into a format that typically takes
>30% less disk space, but the file remains directly executable from DOS.  It
>compresses your file and then prepends an 800 byte decompressor to the front of
>the compressed data.  When you execute the program, the decompressor is
>triggered and loaded into memory.  It then dynamically relocates into high
>memory, loads, decompress, and executes your program.

Executrix, PKLITE, and LZEXE will probably have problems with some .exe files.
I know that at least one word processor (Word Perfect I *think*) doesn't load
all of the exe file into memory at once.  Also, with Turbo Pascal 5.5, you can
concatenate the overlay files onto the end of the .exe file (makes for a big
.exe, but it's easier to keep track of one file than many).  I would expect them
to have problems with .exe files that are created this way.  

I seem to remember reading that certain viruses were having problems (a virus
with a bug is still an interesting concept :-) with the word processor as well.
From what I understand, the first 3 bytes or so of the .exe file tells DOS
how many bytes of the .exe file to load into memory.  The virus was using this
info, and subsequently messing up the .exe file (making it irreperable, any
way).

I wouldn't be surprised to see the .exe compressors having problems with the
built in overlays at first, though I'm sure they'll catch on quickly.  

Hmm... just think... Borland and Micro-Soft might come out with versions of 
their compilers that will have a compression option.  Another space vs speed
consideration.  Would also be harder to step through certain programs in
order to get around the copy protection (though I'm sure that within a couple
months, someone would write a program that would dis-assemble even compressed
.exe files).

Oh well, if you do use these .exe compressors, be sure you keep the originals,
and try to test out every feature of the program just to make sure everything
works ok.
-- 
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