PowerPC G5

The PowerPC G5 (970) is a brand name that was used by Apple Computer for the 5th and final generation of microprocessors from the PowerPC line. Unlike previous generation PowerPC processors from the AIM alliance, Motorola (later Freescale) did not make any G5 processors; these were produced solely by IBM.

The G5 was used in the iMac G5 and Power Mac G5, the latter being advertised as the first 64-bit desktop computer. However, issues with the processor design eventually caused Apple to switch to Intel processors.

Development
The PowerPC 970 series was derived from IBM's 64-bit POWER4 architecture. It can fetch and decode up to eight instructions, dispatch up to five to reserve stations, issue up to eight to the execution units and retire up to five per cycle.

Processors

 * PowerPC 970 — the original G5 was used in the first Power Mac G5 desktop computers in June 2003. Like the preceding PowerPC G4, they include support for the AltiVec instruction set. They do not include a L3 cache, because the front side bus speed, and therefore the main memory, is run at the same speed.
 * PowerPC 970FX — manufactured under a smaller 90 nm process to reduce heat and power requirements, this variant was introduced in the Xserve G5 and iMac G5 in 2004, as well as newer dual processor Power Mac G5 models. However, heat and power issues prevented the G5 from being adopted in a PowerBook, which Steve Jobs had promised in 2003.
 * PowerPC 970MP — code-named "Antares", a dual-core variant of the 970FX with twice as much L2 cache per core. Two 970MP processors were used in the 2.5 GHz "quad-core" Power Mac G5. Clock speeds were expected to surpass 3 GHz, but never did.

Other versions

 * PowerPC 970GX — a single core version of the 970MP retaining the larger L2 cache. It was expected to reach 3 GHz, but would have required 85 W to do so and was cancelled.
 * Xenon — a 3.2 GHz version with 3 cores that was used in Microsoft's XBox 360 console. Because the PowerPC 970 was based on the same architecture, the Power Mac G5 was used as an early development station. The cores incorporated a modified version of the Cell processor, another PowerPC derivative being used in Sony's PlayStation 3 console, forcing IBM to "hide" their work on Xenon from their other partners, Sony and Toshiba.