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 …

Notes on PKLITE format, Part 4

I've decided to postpone writing more about the messy details of PKLITE EXE files, and instead discuss PKLITE COM format. This post is part of a series. For a list of other posts, see Part 1. You may know that the DOS operating system supports two binary executable file formats: EXE and COM. The PKLITE …

Ambiguity of some infinite math expressions

I've come to realize that I don't actually know precisely how to interpret some infinite math expressions with an ellipsis ("…"), like $latex \sqrt{1 + \sqrt{1 + \sqrt{1 + \dots} } }$ First, to flatten out the syntax, I'll define $latex R$ to be the square root function: $latex R(x) = \sqrt{x}$. Now evaluate the …

Notes on PKLITE format, Part 3

For an introduction, and a list of the other posts in this series, see Part 1. Code image compression format Prerequisites: This section assumes you already understand how to decode (non-adaptive) Huffman-coded (or "prefix-coded") data, and how to decompress LZ77-compressed data.Please at least read the notes near the end of Part 2 of this series, …

Notes on PKLITE format, Part 2

For an introduction to PKLITE, and a list of the other posts in this series, see Part 1. This post uses some of the EXE jargon defined in my post on DOS EXE format. Structure of PKLITE-compressed files Here's a bird's eye view of how PKLITE transforms a DOS EXE file when it compresses it: …

Notes on PKLITE format, Part 1

I've been writing (as a feature of Deark) a decompressor for DOS EXE files compressed with PKLITE. Before I forget it all, I decided to write down some of the things I've learned about PKLITE. This is the first post in a series. Other posts: Part 2 Part 3 (compressed data formats) Part 4 (COM …

A quick overview of DOS EXE file format

This is a brief introduction to, and a diagram of, the basic structure of the EXE executable file format used by MS-DOS and some other operating systems. DOS EXE is a subset of the PE "Portable Executable" format still used by Microsoft Windows today, so this also constitutes preliminary information that could be helpful to …

Testing some LZ77 compression limits

This post is about data compression algorithms that involve LZ77, or a similar kind of compression. It's mainly about old-school compression algorithms and software. There is some information about LZ77 in my post about LZ77 prehistory. I won't explain it in detail here, but here are some things to know about it. Both the compressor …

Ways things can rotate

This is an overview of some of the kinds of rotation an object can undergo, with a focus on astronomical objects. Standard warning: I'm starting to realize that I don't really know enough about physics to write about this. But I try not to let things like that stop me. Things to note: I'm discussing …

Differences between females and males

What statistical differences, in body and behavior, does science predict we might observe between females and males of the same species? It's not a safe topic for casual conversation, but it's one that I think is interesting. I'll consider whether it's plausible that such differences might exist, and if so, why. I'll try to keep …