How exactly are the password hashing functions in the pgcrypto module different from the regular MD5 and other algorithms?

This is not technically a database question, but about the innards of Postgres's pgcrypto extension .The documentation says > The algorithms in crypt() differ from the usual MD5 or SHA1 hashing > algorithms in the following respects: I would like to know how/where might I be able to find the details of the hashing algorithms. Ideally, I would like to compare the algorithms of pgcrypto with the regular versions of the algorithms.