noisetonepause wrote:
As I understand it, all the Apple 'Gs' were Power4-derivatives... G3 was 32 bit, G4 was 32 bit + AltiVec, and G5 was 64 bit + AltiVec.
You got the last one right

G3 has nothing to do with POWER4, it is a follow on to the PPC603e processor co-developed by IBM and Motorola. The contemporary server/workstation chip from IBM at the time was the 64bit POWER3.
G4 was a G3+Altivec. The Altivec unit was designed by Motorola.
G4 stagnated in performance for a long time so Apple tapped IBM to develop a desktop version of the POWER4 64bit server chip. This was officially called PPC970 and Apple called it the G5.
The PPC970 took one of the cores of the POWER4 (the first dual core chip when introduced in 2001) and added Altivec (POWER4 didn't have Altivec). PPC970 also cut down on the bus and memory interface speeds compared to the POWER4.
Later on there was the PPC 970MP which was a dual core version of the G5 (the Powermac quad used 2 of these chips). This was still based on the POWER4+Altivec. However, by then IBM was selling POWER5+ chip in their servers/workstations. POWER5/+ was a big advance on POWER4 in that it had
- Vastly greater memory and cache bandwidth
- Lower memory latency due to on-die memory controller
- SMT (2 threads per core).
There was never an "Apple" desktop version of the POWER5 chip.
And now IBM has just introduced the POWER6 which is a kiss-ass processor. Interestingly, the POWER6 now includes Altivec (first POWERx chip to have it) as well as a decimal floating point unit.