No more mysteries: Apple's G5 versus x86, Mac OS X versus Linux
by Johan De Gelas on June 3, 2005 7:48 AM EST- Posted in
- Mac
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) |
32 |
64 |
64 |
64 |
Number of transistors (Million) |
33 |
58 |
169 |
106 |
Die Size (mm²) |
106 |
66 |
+/-130 (112 for 1 MB L2) |
115 |
Maximum Clockspeed (MHz) |
1400 |
2700 (liquid cooled) |
3800 |
2600 |
Pipeline Stages ( fp) |
7 |
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 |
2 |
4 (3 sustained) |
3 |
Floating point issue rate (IPC) |
1 |
2 |
1 |
3 |
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 |
1 |
2 |
2 |
2 |
"instructions in flight" (OOO Window) |
16 |
215 (100) |
126 |
72 |
Branch History Table size (entries) |
2048 |
16384 |
4096 |
16384 |
L1-cache (Instruction/Data) |
32 KB/32 KB |
64 KB/32 KB |
12k µops (+/- 8-16 KB)/16 KB |
64 KB/64KB |
L2-cache |
256 KB |
512 KB |
2048 KB |
1024 KB |
L3-cache |
2 MB DDR SRAM 64 bit at 1/4 th of core clock |
none |
None |
none |
Front Side Bus (MHz) |
166 |
1350 (675 DDR) |
800 (200 Quad) |
N/A |
Front Side Bus (GB/s) |
1.3 Half Duplex |
10,8 Full Duplex |
6.4 Half Duplex |
N/A |
Memory Bandwidth (GB/s) |
2.7 |
6.4 |
6.4 |
6.4 |
Core Voltage |
1.6V |
1,1V ? |
1.38V |
1.4V |
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.
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tfranzese - Friday, June 3, 2005 - link
Kind of snappy there Johan.I do prefer numbers coming from one source myself.
JohanAnandtech - Friday, June 3, 2005 - link
Rubikcube: Speculative? Firstly, Both a webserver and a database server show terrible performance. Secondly, LMbench shows there is definitely a problem with creating threads. So everything point into our "speculative" conclusion.Thirdly, as mentioned in an earlier post:
http://www-106.ibm.com/developerworks/linux/librar...
is another indication that there is nothing speculative about our conclusion.
rubikcube - Friday, June 3, 2005 - link
#21 I disagree. Most of the end of the article on the threading problems was speculative. We can't say that's the cause without actual testing.Jalf - Friday, June 3, 2005 - link
To those wanting a Linux on G5 test, keep in mind the entire purpose of this article. It was to test the performance of a Mac computer running a Mac OS, compared to a Intel/AMD PC.So while installing Linux on the G5 would give us a better idea of how the CPU itself performs, it would also leave out the huge effect the OS also has (You wouldn't have seen the huge performance problems with threading, for example.)
Jalf - Friday, June 3, 2005 - link
#11: Not true, if you browse AMD's documentation for a bit, they do say that their TDP *is* the absolute max power.Intel uses the "maximum power achievable under most circumstances"-method though.
rubikcube - Friday, June 3, 2005 - link
I agree that linux should have been used for a more normalized comparison. I also think that you should have tried running your mysql tests from darwin on x86. You might have been able to find the cause of the performance anomalies.Sabresiberian - Friday, June 3, 2005 - link
I find it hilarious that someone calling him- or herself 'porkster' is complaining about someone else's language :)Apple's computers have made their fame on their user-friendliness, so I think it is very appropriate to compare these computers with OSX on the Apples, as that's where the user-friendliness resides and both OSes are in the same family. It would have been fun to compare using the 64 bit Win XP Pro - I bet we would all get a good laugh out of that. Microsoft is determined, I think, to make a Linux man out of me yet :)
kresek - Friday, June 3, 2005 - link
waiting for AnandTech's YDL results, have a look at this:http://www-106.ibm.com/developerworks/library/l-yd...
SMOG - Friday, June 3, 2005 - link
#13 Thresher: "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."Your right, and those people didn't read this article, at best they read the first page then skipped to the last to see if he bashed Apple or not. This article was for those who want to know just what the power of the PowerPC actually is. This is a technical artical, not a buyers guide. This is science.
Good Job.
CU - Friday, June 3, 2005 - link
You mentioned most people don't use the Intel compiler, but it would have been nice to see it and also the windows compiler and the ibm compiler.