Compress File -- MacCompress Format

  Compresses both forks of a file, replacing the original with a MacCompress file with an identical name.   You may compress any file except MacCompress files and files ending in ".z" or ".Z"; these are assumed to already be compressed.

  The percent compression shown is the total for both forks together.  Thus if your original file has a total of 100 bytes in its data fork and resource fork, then 40% compression means the the output file is a total of 60 bytes.