Working with ZIPPED Files
Files with a .zip extension are compressed files. They must be uncompressed before they can be used. Compression facilitates storing a number of computer files in a single file, and makes the file up to 90 percent smaller than the original file(s). Thus, this format is extensively used for making files available for downloading from an on-line source.
The zip files on the OPM website are compressed with PKZIP version 2.04g or WinZIP. In order to use these files, you will need an uncompression (unzip) program. There are a number of uncompression programs available from the various shareware sites on the Internet. Just make sure that the one that you download can handle PKZIP files.
Compressed files with an .exe extension are self-extracting zipped files. They are created for use on MS-DOS machines running DOS or Windows 3.1 or higher (the compressed files containing Windows software are created to be uncompressed from within Windows only). Running one of these files from the DOS command line or from within Windows will uncompress the files. No special uncompression software is required.