Notes on PKLITE format, Part 7: v1.20 compression

This is a continuation of my series on PKLITE executable compression format for DOS. For a list of other posts, see the first post. In particular, Part 3 is an important prerequisite. In a previous post, I named a then-unknown compression scheme "PKLC-U". In this post, I'll call it "v1.20 compression". I'll refer to all …

ColoRIX compressed 16-color format

This is a follow-up to my previous post on ColoRIX compressed 256-color images. Here I'll explain how to decode (at least some) compressed 16-color images. The short answer: The compression for 16-color images is the same as for 256-color images, except that the "XOR filter" step doesn't happen. The documentation for "RIX3" format (or "new" …

ColoRIX compressed image format

[Update: See also the follow-up post about the 16-color format.] There's an old DOS program named ColoRIX VGA Paint. It was developed by RIX Softworks in the 1980s. Its native graphics file format, which I'll call "RIX" format or "ColoRIX" format, can be read by a fair number of old DOS graphics utilities, and even …

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" …

Notes on SGI image format

There is an old image file format called (among other things) "SGI image". In this post, I'll take a look at it, and make some suggestions about how to decode it. I have no particular reason to care about this format; it's just one that I was studying recently. SGI image is a low-tech still-image …

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 …

Notes on PKLITE format, Supplement 1: Descrambling

This post is part of a series about PKLITE format. For a list of all the posts, see the first post. In a previous post, I noted that some PKLITE-compressed executable files are more difficult to deal with, because most of the decompressor is obfuscated. I named the obfuscation format "scrambled". In this post, I'll …

ARJ compression method 4

ARJ is a compressed archiver utility and format, with features similar to ZIP. It seems at first to have five compression methods, with ID numbers 0 through 4. Method 0 is for no compression, so it's easily dealt with. Methods 1 through 3 are really all the same. They record how hard the compressor tried …

Survey of RAR comment formats

This post is about RAR, a file compression and archiving file format in the same category as ZIP. It's known for its association with the WinRAR software, but there are also command-line and text-mode versions of the software that are just named RAR. RAR supports two kinds of comments: A main "archive comment", for the …

Which comes first in DOS timestamps, the date or the time?

There are a lot of old DOS-centric file formats, especially file archiving and compression formats, which store timestamps of files. Most of them use the standard MS-DOS timestamp format for such things. This format is usually interpreted as two 16-bit integers: one for the date, and one for the time of day. I'm not sure, …