Technically, since about 1998, 1 giga = 1000 mega of
anything and 1 gibi = 1024 mebi of
anything although some people still use mega and giga when they should be using mebi and gibi...
See NIST definition:
http://physics.nist.gov/cuu/Units/binary.htmlSo 1 gigahash/second = 1000 megahashes/second and 1 gibihash/second = 1024 mebihashes/second
Also note that 1 mebihash/second = 1,048,576 hashes/second and 1 megahash/second = 1,000,000 hashes/second.