According to the rules of the contest, an entry must consist of both the compressed data and the decompression program packed into one of several standard archive formats. Time and memory limits, archive formats, and decompression languages have been relaxed over time. Currently the program must run within 24 hours on a 2000 MIPS machine under Windows or Linux and use less than 800 MB memory. An SHA-1 challenge was later added. It allows the decompression program to output files different from the Calgary corpus as long as they hash to the same values as the original files. So far, that part of the challenge has not been met.