Notes on CompuShow

CompuShow is an image viewer software product, developed by a small company named Canyon State Systems and Software. It was maintained from around 1987 to 2001. It was for DOS, and later Windows. I think the DOS version was fairly popular, at least for a while. It has some historical significance. As of this writing, … Continue reading Notes on CompuShow

Analyzing some encrypted ARJ archives

There's an item in the Internet Archive's software collection, which someone uploaded and named "EPS CD 2 German 1994". https://archive.org/details/eps-cd-2-german-1994 It contains a few hundred .EXE files, organized in a handful of directories. And that's all. There's no explanation of what it is. No documentation. Not even a picture of the CD-ROM that it was … Continue reading Analyzing some encrypted ARJ archives

Notes on writing “magic” patterns for the “file” command

The file command is a classic Unix-centric utility that guesses the format of a file, based only on the file's contents. It may also print some additional information about the contents of the file. The modern open-source version of it can be found at <https://darwinsys.com/file/>. Other posts about the file command: A script to analyze … Continue reading Notes on writing “magic” patterns for the “file” command

Some notes on NP and NP-completeness

Most everyone who has some interest in math or computer science has heard of the P vs. NP problem, and the concept of NP-completeness. Problem classes P, NP, and NP-complete are fundamental to the field of complexity theory, are there are many good introductions to them. This post is not going to be a good … Continue reading Some notes on NP and NP-completeness

Survey of LZW compression schemes

LZW is a kind of data compression. I'm not much of a fan of it, but I've learned about enough LZW variants that it might be interesting to compare them. Note that there are many other LZW variants in existence, that I don't know much about, so I can't promise that this is a good … Continue reading Survey of LZW compression schemes

Notes on bit order

Most of the time, reading a computer file involves interpreting it as a sequence of bytes. However, there are some "bit-oriented" formats that are best thought of as a sequence of bits, instead of bytes. In this post, I'll go over the basics of such formats. It's usually not the entire file that is bit … Continue reading Notes on bit order

Win32 I/O character encoding supplement 3: UTF-8 manifest

For a list of other posts in this series, refer to the first post. A relatively recent Windows software development feature, affecting character encoding, is the ability to request a specific "ANSI" character encoding (or "code page"), presumably UTF-8, using a manifest. I decided to investigate what this really does. This "manifest method" is independent … Continue reading Win32 I/O character encoding supplement 3: UTF-8 manifest

Updated survey of LHarc and LHA

Since my first post on DOS versions of LHarc/LHA, I've found a few more versions of the software. Six of them appear to be original/official, and all of those are Japanese-language: 1.13d, 2.05b, 2.13, 2.52, 2.54, and 2.55. And I found quite a few new modified or hacked versions, two of which I'll discuss: "v1.14a" … Continue reading Updated survey of LHarc and LHA

Survey of EXPAND/DECOMP utilities

If you look at old DOS and Windows software distribution disks, you may see a lot of files whose names have the last character replaced by a "_" character, or sometimes a "$" character. For example: mplayer.ex_ mplayer.hl_ mplayer.re_ msacm.dl_ msacm.dr_ msadpcm.ac_ mscomstf.dl_ ... Many such files belong to a family of compressed file formats … Continue reading Survey of EXPAND/DECOMP utilities

What is LZSS compression?

I'm not asking how to implement LZSS. I'm asking how to distinguish things-that-are-LZSS from things-that-are-not-LZSS. It's generally understood that LZSS is a kind of data compression. It's supposedly a derivative of LZ77. But you may struggle to find out anything definitive or verifiable about LZSS. The name LZSS is more than likely derived from Lempel–Ziv–Storer–Szymanski, … Continue reading What is LZSS compression?