Zip is a compression and archiving format. It is useful not just for compressing files so they take up less space (and thus take less time to download), it also allows multiple files to be saved in one zip archive, making distribution of sets of files easier.
"Zip puts one or more compressed files into a single ZIP archive, along with information about the files (name, path, date, time of last modification, protection, and check information to verify file integrity). An entire directory structure can be packed into a ZIP archive with a single command. Compression ratios of 2:1 to 3:1 are common for text files."To unzip files in zip format you will need appropriate software.
As a dos user I use PKZIP version 2.04 for DOS and Winzip as a Windows front end. PKZIP 2.04 is actually a suite of dos programmes - pkzip for compressing files, pkunzip for decompressing them, and pkzipfix for fixing damaged zip files. WINZIP is a windows shell which makes using PKZIP 2.04 a lot easier.
There is a PKZIP for Windows, (seperate versions for Windows 3.1 and Windows 95) however the current release does not create archives across multiple disks unlike PKZIP 2.04 for Dos and Winzip.
Beware a "version" 3.0 of PKZIP which is actually a fake containing an unpleasant virus. There is no version 3.0. of PKZIP.
There are alternative zip programmes for Dos and Windows, and for every other platform.
Info-zip is available in versions for Mac, Amiga, Atari, Unix and many others. (Its also free rather than shareware). However it also cannot save files across multiple disks. Here is a useful webpage about it, with lots of links.
[http://quest.jpl.nasa.gov/Info-Zip/Zip.html]
All these files are available widely - here are some links to the Demon ftp site in London. You may prefer to look for a more local archive.