What Makes Apple's Power Mac G5 Processor So Hot

An anonymous reader writes "58 million transistors can drive a lot of power. Apparently, Apple appreciated the choices IBM processor architects made when designing the 970 family. This article provides the 64-bit architecture big picture for the 970 family (A.K.A. the Power Mac G5) and the critical issues in IBM's 64-bit POWER designs, covering 32-bit compatibility, power management, and processor bus design."

Comments

Re:64 bit integers

[francisew]

More importantly, it doesn't have to break the 64 bit operations into many successive 32 bit operations. 64 bit operation are not simply 2x32 bit operations, but can be several dozen operations.

An 8-bit microcontroller can perform 64 bit floating point operations correctly. It just takes a long time.

Re:WATT figures for G5 vs AMD-64?

[Anonymous Coward]

It's hard to make a comparison because for some reason IBM/Apple doesn't want to release official measurements for power usage. Which is strange because they should do really well in that measurement compared to AMD and Intel. Here's their official numbers:

2.4 GHz A64- 89 W
3.4 GHz P4(Northwood)- 89 W
3.4 GHz P4(Prescott)- 103 W

Best guess on the 2.5 GHz G5 is around 65 W.

Re:ob Memory

[Mark_in_Brazil]

18 exabytes ought to be enough for anybody

-GillBates0, 2004

So where does it end?

This page makes a fairly convincing argument that 256 bit CPUs should be enough (basically, there would be no way to exhaust the amount of memory a 256 bit CPU could access, because the number of memory locations is about the same as the number of atoms in the universe).

--Mark

Re:64 bit integers

[Waffle Iron]

Since floating point registers in most modern CPU's are 64-bit wide already.

Actually, since most modern CPUs are x86 variants, the floating point registers are usually 80 bits wide (and have been since the 1981 introduction of the 8087).

As far as "complex mathematical calculations" go, 64-bit integers aren't really that big a deal. It's pretty rare to need integers bigger than 2^32 but no bigger than 2^64; floating point usually handles big numbers more flexibly.

The big deal with 64-bit CPUs is 64-bit address pointers and operations on them (which usually aren't more complex than adding and shifting).

Good followup link from the article

[C.Batt]

Introduction to 64-bit computing

There's an informative link at the bottom of the article for those requiring a bit more insight into the effect of 64-bit computing. /wishes he had exa-bytes of memory right now... VS.NET on WinXP is a PIG!