PPM Compression

For compression of archives and transport of large files, it is worth trying PPM "Prediction by Partial Matching" (http://en.wikipedia.org/wiki/Prediction_by_Partial_Matching).

To install in Linux (though the author does not recommend this application for general use):
sudo apt-get install ppmd

For help:
man ppmd

To compress the file archive.tar (creates archive.pmd):
ppmd e archive.tar

Incredibly slow but can be twice as compressing as zipping. A good trade-off for longterm backups. However in simple tests on binary files it did not perform as well as bzip2 or lzma (http://en.wikipedia.org/wiki/LZMA) which gave best results for general files. The author does explain in the man file that his program is optimised for natural language rather than "noisey" files.