High Quality Content by WIKIPEDIA articles! PCI-X, short for PCI-eXtended, is a computer bus and expansion card standard that enhances the 32-bit PCI Local Bus for higher bandwidth demanded by servers. It is a double-wide version of PCI, running at up to four times the clock speed, but is otherwise similar in electrical implementation and uses the same protocol. It has been replaced in modern designs by the similar-sounding PCI Express, with a completely different connector and a very different logical design, being a single narrow but fast serial connection instead of a number of slower connections in parallel. There is also a 64-bit PCI specification electrically different but with the same connector as PCI-X.