Gzip'ed Tar Archive vs a Zip (or other compressed) Archive ------------------------------------------------------------ What we are taking about ... First of all `zip' is a compression algorithim name, for the Lempel-Ziv compression algorithm, it does not really have anything to do with archiveing multiple files into one single file for storage. Zip (or PKzip) is also the name of a program which compresses files and stores the files in a archive. IE: the files are compressed and then archived. The advantage and the reason why they do this is that you can then archive and de-archive individual files to and from the archive easily. GZip is a compression program, NOT and archiver. That is it compresses files, not merge multiple files into one file. Tar is often used with gzip as the archiver especially as tar does not do any compression itself. IE: tar is a pure archiver and gzip is a pure compressor. By using both tar and gzip together, that is, tar the files into a single archive file, then gzip (compress) the tar archive, you can usually get even better compression that using a archiving program which does both tasks (like PKzip). That is because the zip compression algorithm is then applied accross ALL the files at the same time, and not on a single file by file basis as with the Zip archiver program. For Example ... I have a huge directory of GIF files for web use. Zip (or PKzip) can NOT compress the GIF files very well. This is because GIF is a run-length encoded format which is a semi-compressed file format. As a result of this pre-compression in the GIF format, the zip compression does not compress files very well on a file by file basis. The Zip archive of all my WWW images results in a 10 MegaByte file! However, by Tar'ing all the images together first, then Gzip'ing them ALL at the same time, you can compress over ALL the images together. This means the `zip' compression algorthim can look for and find common stings between the semi-compressed GIF files. Thus the archive instead of 10 MBytes can be reduced to an archive of about 1Mbyte in size. Or one tenth ( 1/10 ) the size of a equivelent Zip archive ! Very very big saving in disk space. The only drawbacks to a GZiped Tar archive is that you can not add files to or extract individual files from an already existing archive. One file can be extracted from the archive but not quickly as Gzip will uncompress the whole archive for tar to then search for and extract a single file. But for distrbuting a common collection of files this is not a required feature so for GIF images a gzip'ed tar archive is much prefered over a zip or pkzip archive. Summery.. PkZip archives using Lempel-Ziv compression (zip) on individual files only. GZiped tars uses the Lempel-Ziv compression over the WHOLE file (or tar archive) and thus can find more to compress than PkZip (5 to 10 times better!). Note a new zip variation now available is bzip2 which compresses even better than gzip. but the cost for this is speed. It is much slower than gzip. For more information of Tar (with Gzip Archives) see the Tar Archive Usage Document