Summary: the cores compared

Below, you find a comparison of the Intel Xeon/Pentium 4, the Opteron/Athlon 4, the G5 and the previous CPU in the Apple Power: the G4 of Motorola.

CPU feature

Motorola G4+

G5 (IBM PowerPC 970)

Intel Xeon P4 Irwindale

AMD Opteron Troy

Process technology

0.18 µ CU SOI

0.09 µ CU SOI

0.09 µ CU

0.09 µ CU SOI

GP Register Width (bit)





Number of transistors (Million)





Die Size (mm²)



+/-130 (112   for 1 MB L2)


Maximum Clockspeed (MHz)


2700 (liquid cooled)



Pipeline Stages ( fp)


16 (21)

31 - 39*

12 (17)

issue rate (Instruction per clockcycle)

3 + 1 Branch

4 + 1 branch

4 ports, max. 6 (3 sustained)

6 (3 sustained)

Integer issue rate (IPC)

3 + 1 Branch


4 (3 sustained)


Floating point issue rate (IPC)





Vector  issue rate (IPC)

2-4 ( Altivec)

2-4 ( Altivec, velocity)

4  Single(SSE-2/3)

4  Single(SSE-2/3)

2 Double (SSE-2/3)

2 Double (SSE-2/3)

Load & Store units





"instructions in flight" (OOO Window)


215 (100)



Branch History Table size (entries)





L1-cache (Instruction/Data)

32 KB/32 KB

64 KB/32 KB

12k µops (+/- 8-16 KB)/16 KB

64 KB/64KB


256 KB

512 KB

2048 KB

1024 KB


2 MB DDR SRAM 64 bit at 1/4 th of core clock




Front Side Bus (MHz)


1350 (675 DDR)

800 (200 Quad)


Front Side Bus (GB/s)

1.3 Half Duplex

10,8 Full Duplex

6.4 Half Duplex


Memory Bandwidth (GB/s)





Core Voltage


1,1V ?



Power Dissipation

30W at 1 GHz

+/- 59 (Typical) -80 Watt (max)

110 W (Typical)

92,6W (Max)

*31 is branch misprediction pipeline length, 39 is the length of the total pipeline including decoding stages before the trace cache.

Let us summarize: in theory, the PowerPc 970FX is a very wide, deeply pipelined superscalar monster chip, with excellent Branch prediction and fantastic features for streaming applications. And let us not forget the two parallel FPUs and the SIMD Altivec unit, which can process up to 4 calculations per clock cycle.

The disadvantages are the rather coarse way that the 970FX handles the instruction flow and the high latency to the RAM.

Enough theory. Let us see how the G5 2.5 GHz and 2.7 GHz compares to the 3.6 GHz Xeon Irwindale and Opteron 250 (2.4 GHz). The Opteron 852 arrived just a day before my deadline, but I think that you will know how the 252 performs compared to the 250. Before we tackle performance, here are a few quick notes about power dissipation.

Power to the PowerPC

How power thirsty is this PowerPC 970FX? His predecessor, the 0.13µ SOI PowerPC 970 was a pretty cool chip. It consumed about 42W at 1.8 GHz (1.3v). The newer 0.09µ SOI PowerPC 970FX CPU is reported to dissipate about 55-59W at 2.5 GHz. However, a few annotations must be made.

First of all, IBM and Apple tend to increase the core voltage when running at higher clock speed. This makes the needed power increase more than linearly. For example, the 1.8 GHz PowerPC 970 consumed 42 Watt, but the 2 GHz version (both 0.13µ CPUs) needed 66 Watt.

Secondly, the TDP IBM talks about is typical , not maximum like AMD's.

Let us clarify this by checking IBM's and Apple's numbers. For the 90 nm, IBM's own documents tell us that the PowerPC 970FX only consumes 24.5 Watt at 2 GHz (1V). However, the same 0.09µ SOI PowerPC970FX is reported to consume about 55W at 2.3 GHz (1.1V?) in the Xserve, according to Apple's own website. Typically, you would expect the G5 to consume about 28 Watt (24.5 * 2.3 / 2) at 2.3 GHz, when using the 24.5 Watt at 2 GHz as a reference. Apple talks about "at most" (maximum), and IBM about "typical".

Still, that is a huge gap between "typical" and "maximum" power dissipation. The 55 Watt number seems to indicate that the core voltage must have been increased significantly at 2.3 GHz. The maximum power dissipation of the 2.5/2.7 GHz G5 inside the liquid-cooled PowerMacs might thus be quite a bit higher than in the 1U Xserve, probably around 80 Watt for the 2.7 GHz. That is a lot of power for a 66 mm² CPU, and it probably explains why Apple introduced liquid cooling. The liquid cooling system inside our PowerMac wouldn't get warm and wouldn't be necessary at all if the two 2.5 GHz CPUs were only dissipating a 59 Watt maximum.

IBM PowerPC 970FX: Superscalar monster Benchmark configuration
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  • michael2k - Friday, June 3, 2005 - link

    Well, it shouts to stay away from the XServe unless you happen to have vectorizable code that you have the resources to properly vectorize!
  • erwos - Friday, June 3, 2005 - link

    Excellent comparison of the platforms, although I actually wish they would have spent more time analyzing the graphs.

    Like the others, I would have liked to see a G5 / Linux benchmark (now that FC4 has a PPC version, you could run a fairly reasonable one), but I do admit it's not a very popular option compared to x86. My curiosity is whether MacOS X is the problem, or whether it's some sort of issue with the CPU itself. Seems unlikely the G5 would have such a fundamental flaw, but it does shout to stay the hell away from the Xserve until these issues are resolved.

  • Thresher - Friday, June 3, 2005 - link

    As the owner of intel, AMD, and Mac based computers, I have to say this is one of the best and most thorough comparisons I've seen.

    You did an excellent job of isolating CPU and OS performance.

    That being said, if performance were the only indicator, there is no doubt in my mind that AMD would be ruling the roost. However, personal preferences come into play to a great deal. Businesses like the reputation behind intel. I prefer the usability of Mac OS X. People have strong feelings about Microsoft that may color their decisions.

    When it comes down to it, performance is important, but not the only reason people buy what they buy. I would say more often than not, the decision is made with only a modicum of logic.
  • Cruise51 - Friday, June 3, 2005 - link

    I'd be interested in seeing how it performs on yellowdog aswell.
  • IntelUser2000 - Friday, June 3, 2005 - link

    People, in case some of you misunderstand, the 10.8GB/sec Full Duplex bus means that its two 32-bit 1350MHz bus, rather than one 64-bit bus in the PCs. Its not, 10.8GB/sec x 2 =21.6GB/sec bus, its 10.8GB/sec bus(or more correctly stated 5.4GB/sec x 2). Plus, it says in Apple site that it has TWO(yes two!!!) of the 10.8GB/sec buses, per CPU.

    Summary: Per CPU=10.8GB/sec
    Per Dual Processor System=21.6GB/sec

    Johan, about the AMD TDP number, they never state that its max power, they say its maximum power achievable under most circumstances, its not absolute max power.
  • JohanAnandtech - Friday, June 3, 2005 - link

    Porkster: It is a little geekisch Unix joke. Where is your geekish you man spirit?

    Wessonality: Our next project if we can keep the G5 long enough in the labs.

    Ailleur2: indeed, I agree. The G5 is a potent CPU with a lot of potential. Just give it a bigger L2 and a better memory subsystem. This is an architecture that could last very long by applying a few tweaks, like the P6.

    Methodical: All of the benchmarks are trustworthy, they should be looked upon as a whole to get a good picture, not just pick one. About After affects, I indicate that the G5 does very well here (seen other reports on the web), I just didn't have the software in the lab.

    I also warned that this was not about "should I buy an Apple or not?". It is just "if performance is what counts for me, where should I position the G5/Mac os X combiantion compared to x86/Linux/Windows ?".

  • StuckMojo - Friday, June 3, 2005 - link

    hmph. you say it yourself in the last come you didn't try it?
  • StuckMojo - Friday, June 3, 2005 - link

    yes, it seems you've left out a very good method of testing if OSX is the issue: run a powerPC linux distro with the mysql and apache benchmarks and see what happens!

    i'd be _really_ interested in the results. see if you can update the article with them.
  • porkster - Friday, June 3, 2005 - link

    "Root Me" in Australian slang is the same as "Fxxk Me" in common language. Some people my find a picture in this review offensive.
  • wessonality - Friday, June 3, 2005 - link

    What about installing Yellow Dog Linux on the XServe?

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