The G5 is a 64-bit member of the PowerPC processor family that is fully compatible with 32-bit code. It was first used when the Power Mac G5 was introduced in June 2003. Only three different versions of the chip were produced before Apple made the move to Intel CPUs in 2006. IBM was the only manufacturer of G5 CPUs.

The first G5 CPU, the PowerPC 970, built on everything IBM had learned in producing its POWER4 CPU for servers. As CPUs designed for servers, low power consumption was not one of IBM’s goals, so the G5 Power Macs all needed very sophisticated cooling systems to deal with the heat the PowerPC 970 created. The computer had a total of nine cooling fans to control temperatures.

• See: IBM PowerPC 970 factsheet (PDF) – (Download, 4 MB)
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• See: IBM970vs970fx.pdf.zip – (Download, 234 KB)

The came 970 with a 64 KB instruction cache and 32 KB data cache – a step forward from using 32 KB for each throughout the G3 and G4 eras (See Page 6 of IBM PowerPC 970 factsheet PDF).
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PowerPC 970 Key Features and Notes

The Power4 was designed with a balanced system/bus throughput design in mind, with native 32-bit compatibility, and a high frequency. The 970 took these design goals a step further, focusing on a smaller die with lower power consumption, and a single CPU core for the first generation.
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(Copyright International Business Machines Corporation 2002.)
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(Source: ISSCC 2004 / SESSION 3 / PROCESSORS / 3.7)
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To improve upon the G4 chips, the design also focused on a high-bandwidth memory bus which featured two unidirectional buses. On a 900 MHz System Bus, for example, the system is able to achieve up to a 6.4 GB/s useable bandwidth.

• Buses carry addresses and control signals in addition to data. You will see a % of peak bandwidth.
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• As the buses are unidirectional, each direction can realize only half the aggregate bandwidth.

(Copyright International Business Machines Corporation 2002.)
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Chip power draw

Official documentation states 19W at 1.2 GHz, and 42W at 1.8 Ghz. More documentation from “ISSCC 2004 / SESSION 3 / PROCESSORS / 3.7” confirms 66W at 2 Ghz for the first-generation 970, and the 1.6 GHz TDP is an estimate.
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A 2 GHz IBM PowerPC 970 has about the same TDP as an Intel Core i7-8700: 65W. If you were to run a Dual 2.0 G5 at the “Highest” performance, and ran a CPU intensive app, it would be like running 2 maxed-out i7 2018 Mac minis in terms of power draw.

Compare to an original Mac Pro: Funnily enough, despite the amount of heat produced/complained about from the Power Mac G5, even the first generation IBM 970 has nothing on the Clovertown Xeons from a 2007 Mac Pro (Only in terms of power draw).

• An Intel Xeon X5365 pulls 150 Watts at maximum, and an 8-core 2007 Mac Pro has two of them. Even so, there is a “PL2” maximum which allows this chip to push all the way to 206 Watts under the absolute heaviest of workloads.
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• A Dual 2 Ghz 2003 Power Mac G5 will only top out at 122 – 150 Watts total between the CPUs. In fact, a base-spec Quad 2.0 2006 Mac Pro uses Intel Xeon X5130s, which have a matching TDP. Better performance-per-watt indeed.
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Performance Benchmarks

SPECint2000

• 937 @ 1.8 GHz (October 2002)

SPECfp2000

• 1051 @ 1.8 GHz (October 2002)

Dhrystone MIPS

• 5220 @ 1.8 GHz (October 2002)
• 2.9 DMIPS / MHz (October 2002)

Additional Performance

• Peak scalar GFLOPS = 7.2
• Peak SIMD GFLOPS = 14.4
• RC5 : 18M keys/sec

Contemporary Benchmarks

• 13.1 GFLOPS (13.1 Billion Operations Per Second) @ 2x 2.0 GHz
  • See: Maximizing an AGP Power Mac G5 into space and beyond: 2025 Edition
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Inside the PowerPC 970 First-Generation (Diagram)

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CPC925 Northbridge Chip

This is an Apple-designed chip made for the Power Mac G5, and used for the first and second generations of PowerPC G5 chips. It is also sometimes referred to as the Apple U3 or U3H (ECC variant) chip, capable of supporting up to two chips. There are two 550 Mhz unidirectional CPU buses, a 400 MHz DDR memory controller, 8x Pro AGP, and a 400 MHz 16-Bit HyperTransport tunnel.

An unfinished prototype version of this Northbridge chip exists called the U3L (U3Lite), which was made in development for the unreleased PowerBook G5.
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Condensed CPU Specs