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

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 … Continue reading Notes on PKLITE format, Supplement 1: Descrambling

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

Notes on some old self-extracting ZIP archives

The old PKZIP compression software for DOS includes a utility named "ZIP2EXE", which turns a plain ZIP file into a self-extracting executable file in DOS EXE format. Depending on the version of PKZIP/ZIP2EXE, and the options used, there are several different ways in which this EXE file is constructed. I wanted to learn about these … Continue reading Notes on some old self-extracting ZIP archives

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?

Survey of LHarc and LHA versions and names

The LHarc family of software (including LHA, etc.) is an old compression and archiving utility, originally for DOS computers. I've found the LHarc version history to be confusing in a number of ways. In this post, I'll try to explain what's what, to the best of my knowledge. LHarc is comparable to its contemporaries PKZIP … Continue reading Survey of LHarc and LHA versions and names