The fifth generation (Get it? Generation 5?) of the PowerPC Archecture that was pioneered by Apple, Motorola, and IBM. Also known as the PPC (PowerPC) 970. IBM alone makes this chip which borrows somewhat from Motorola's G4 and IBM's own Power4. Said to be the first 64 bit processor for personal computers and has a 2:1 processor frequency/front side bus ratio. For instance, a 2.0 GHz G5 has a FSB of 1.0 GHz. It is currently used in IBM's own BladeCenter servers and Apple's PowerMac, Xserve, and is rumored to debut in the iMac soon. While Apple has yet to ship a true 64 bit OS, Mac OS 10.2.7 and up uses 64 bit extensions which allows it to break the 4 GB barrier of 32 bit chips and address a full 8 GB memory. Due to excessive heat, the 2.5 GHz G5 had to be liquid cooled and a Powerbook version isn't expected soon. At its debut it used a 130 nanometer process but the 2.5 GHz model and the Xserve models use a smaller 90 nm process. A couple Supercomputer clusters have been built utilizing the G5, including Virginia Tech University, COSLA (a US Army contractor), and now UCLA.
Dude, that G5 owns your Pentium!
The G5 is the fifth generation of the PowerPC line.