Survey of PKZIP versions for MS-DOS

I wanted to know exactly what versions of the old PKZIP compression software were publicly released for MS-DOS, and some basic characteristics about them, particularly what compression methods they used when compressing files. Sure, Wikipedia has a list, but it wasn’t quite what I wanted, and it omitted at least one version I was pretty sure existed.

So, I did some research, which included:

  • Downloading all the versions I could find.
  • Scanning their documentation for references to previous versions.
  • Web searches for likely filenames of version numbers that might or might not exist.
  • Running each version in DOSBox.

Results

VersionDistribution filenameDateCompression methods
0.80 (beta)?1989-01-10Store, Shrink, Reduce
0.90PKZ090.EXE1989-02-10
0.92PKZ092.EXE1989-03-06
1.01PKZ101.EXE1989-07-21Store, Shrink, Implode
1.02PKZ102.EXE1989-10-01
1.10PKZ110.EXE1990-03-15
1.93 (alpha)PKZ193A.EXE1991-10-15Store, Deflate
2.04cPKZ204C.EXE1992-12-28
2.04ePKZ204E.EXE1993-01-25
2.04gPKZ204G.EXE1993-02-01
2.50PK250DOS.EXE1999-03-01

I’m 60% sure that this list is complete, even though the version numbers are all over the place.

General notes

  • All of the versions display a date in their help screen, and that is the date I give in the “Date” column. I can’t be sure that the software was actually released on exactly those dates.
  • As far as I know, all versions can decompress all the compression methods used by previous versions, regardless of whether they can compress new files using those methods.

Notes on specific versions

0.80

I don’t know what form this was distributed in. I found it in a file named PKZ080.ZIP, but that can’t have been how it was originally distributed, because how would you unzip it?

It’s not even completely clear to me that this was public beta, as opposed to a private beta that got leaked.

Wikipedia claims a release date of 1989-01-01, which is not consistent with my findings. But it’s possible that the embedded dates are misleading, or that I don’t have a good copy of it, or that there were multiple releases.

0.90

Despite the 0.x version number, this and 0.92 appear to be full releases, not previews or beta tests.

1.10

I wrote a whole post about the different PKZ110.EXE files found in the wild.

1.93

This was a preview release, and the first release to support Deflate (method 8) compression, though it wasn’t named Deflate yet. Or was it? The documentation doesn’t give it a name, nor does the software when you use it to list the contents of a ZIP file. But when you use the software for compression and decompression, it prints the words “Deflating” and “Inflating”.

2.04c

Despite the unlikely-looking version number, I believe that v2.04c was the first 2.x release. Wikipedia offers a partial explanation: It was to reduce potential confusion with some fraudulent versions that were floating around.

2.50

Wikipedia says that v2.50 supports decompressing Deflate64 (method 9), though this feature does not appear to be mentioned in the documentation.

This is said to be the final MS-DOS version, but I say, hey, there’s no law against making new MS-DOS software in 2019.

Who, me?

I’m sure I’m not the first to notice the secret message in the 0.x versions of the PKUNZIP.EXE file. From 0.92:

The message does not appear in later versions. Well, I guess it’s possible it’s still there in some form (maybe compressed), but, at least, it’s not readily visible.

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