He was referring to an option to GNU's tar. It just automatically compresses the entire archive using gzip or bzip2 after the archive has been generated. Saves a little intermediate disk space because it doesn't have to write an intermediate file. The usage ``tar zcf archive.tar.gz [files]'' is roughly equivalent to ``tar cf - [files] | gzip -c > archive.tar.gz''.

By the way, most compression algorithms work much better on a large set of data than a small set, which is one reason why the compression is performed on the entire archive instead of the contained files.

Also, few people actually use tar to write to tape any more. There are usually more uselful utilites with more features and fewer bugs elsewhere. Your filesystem's dump utility and cpio come immediately to mind.