One of the dark corners of ZIP file format is the "multi-segment" archive feature. By "multi-segment archive", I mean to include the disk spanning features intended for floppy disks, and the slightly more general case of "split archives", which was added to the format documentation around the year 2000. The idea is, what would normally … Continue reading Notes on ZIP format and disk spanning
Tag: zip
Notes on PKZIP for Windows 3.x
I've made some posts about PKZIP for DOS (for example, see my old post on PKZIP versions), and about PKLITE-compressed files for DOS (I have a series of posts about it), but I'd kind of stopped there. I thought it would be a good idea to continue on, and research at least PKZIP for the … Continue reading Notes on PKZIP for Windows 3.x
Fixing a hidden bug in PKZIP 2.04c
The non-clickbait title of this post is Notes on PKLITE format, Supplement 2: Not enough memory. This post is part of a series on PKLITE format. For a list of all the posts, see the first post. See the end of this post for links to most of the software mentioned in it. If you … Continue reading Fixing a hidden bug in PKZIP 2.04c
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
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 … Continue reading Testing some LZ77 compression limits
PKZIP Implode bug #3
I've already written about two PKZIP bugs related to the "Implode" compression method. Now I've come across another one, so I guess I'll investigate it as well. Here are the first two: Bug #1 (MML)Bug #2 (v1.01 literal tree issue) There's an old collection of files called the Pier 1 Shareware CDROM (#1). On it … Continue reading PKZIP Implode bug #3
Another Implode bug in old PKZIP software
In a previous post, I discussed an old PKZIP bug related to the compression method named "Implode". I'll call that bug the "MML bug", for "Minimum Match Length". [See also a later post: Bug #3.] In this post, I'll discuss another old PKZIP bug related to Implode compression, mainly just to distinguish it from that … Continue reading Another Implode bug in old PKZIP software
Investigating an UnZip decompression bug
One of the old compression methods for ZIP format is named "Shrink". In the process of writing my own Shrink decompressor, I came across a problem with the Info-ZIP UnZip software. It's triggered by a small percentage of Shrink-compressed files. As an example, I'll use the file that you can download here: BLING.WAV. Now, in … Continue reading Investigating an UnZip decompression bug
PKZIP “Implode” compression oddity
When I was researching old versions of PKZIP, I found that modern unzip programs aren't able to unzip the PKZIP v1.01 distribution file. Three of the member files inside the self-extracting ZIP file fail to decompress correctly. /cygdrive/c/dosprogs/ZIPTEST/101 $ unzip ../DIST/PKZ101.EXE exploding: README.DOC warning: 475 bytes required to uncompress to 873 bytes; supposed to require … Continue reading PKZIP “Implode” compression oddity
An un-unzippable ZIP file
Apparently, I'm writing a series of articles about ZIP format. Here's a curiosity. I'm going to use the Info-ZIP zip program to make a ZIP file that the Info-ZIP unzip program cannot unzip. I'll only do things that should be benign, i.e. things that a normal user might conceivably do. This article assumes you have … Continue reading An un-unzippable ZIP file
Entropymine 