Contributors are encouraged to submit material in this format. Files ending with the .gz suffix were compressed using 'gzip'. Files ending with the .Z suffix were compressed using 'compress'. Files of this format will be converted to 'gzip' format, eventually. This is a format is common for MS-DOS files.
Files ending with the .tar suffix are multi-file archives, archived using 'tar'.
These are commonly compressed using either 'gzip' or 'compress', and will instead have a .tar. Z or .tar.gz suffix, as appropriate. These will gradually be replaced by gzipped tar files. These are commonly compressed using either 'gzip' or 'compress', and will instead have a .ps. Z or .ps.gz suffix, as appropriate.