G4
From Mac Guides
G4 refers to the 4th generation of the PowerPC architecture. It was used in PowerBooks, G4 towers, and the iMac G4, Mac mini, iBook. In more powerful applications, it was replaced by the G5 - although remained in use for PowerBooks because of its low power consumption. The G4 name was distinguished from the G3 name because of its use of AltiVec technology. Apple commonly used the G4 in dual processor configurations.
The G4 processor was used in the following Apple models:
Revisions
Their are two main subsections of G4 CPU the G4 and the G4e. The G4 had to be majority redesigned to break the 500MHz barrier in order to remain competitive with other processor manufacturers. The main difference between the G4 and G4e is in the pipeline: the G4 has a 4 stage pipeline the G4e has a seven stage pipeline. The added pipeline stages had a slight performance effect on the G4e, which is why a 500MHz G4 can still compete with a ~650MHz G4e. The G4 and G4e processor is produced by Motorola/Freescale. The G4 had many revisions, some still used by processor upgrade companies today:
- 7400: 250nm
- 7410: 180nm (die shrink)
- 7450: 256K on die cache
- 7455A/B (revisions of the 7450 with no major changes just faster clock speeds)
- 7445 (low power version of 7450 without the L3 cache controller)
- 7457: 130nm revision with 512K on die cache
- 7447A/B (version of the 7447 up to 1.6GHz)
- 7448 (e600): 90nm 1MB cache version of the 7447A, complete with 200MHz bus (not currently in use in any Apple product)
Dual core versions of the G4 also exist that Freescale is currently sampling, but these chips are all these chips share with the G4 is the execution core itself, they use a different bus, a different socket, and a different expansion bus, so apple would have to create a completely new logic board design to use them, something that is doubtful with the switch to x86 looming ahead.
Freescale also produces G4 CPUs that are faster than what they advertise, but because of Apple's demand they are in such short supply that they simply cannot advertise them. Such is the case with the 7447B which can go up to 1.67GHz, and was the case with the 7455B which Motorola advertised to only go up to 1.25GHz, but Apple bought faster processors from them.
