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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Reflex - Friday, June 3, 2005 - link
NT was designed primarily by Dave Cutler, who was one of the guys behind VMS at DEC. NT is not based on Mach and has no relation to it, although it shares some similarities with BSD and VMS.tfranzese - Friday, June 3, 2005 - link
#35, Apple's platform uses HT links (don't ask me specifics).minsctdp - Friday, June 3, 2005 - link
What's with the 24 MB/s memory write time on the Xeon, vs. nearly 2GB/s for the others? Looks bogus.querymc - Friday, June 3, 2005 - link
I'd still like to see a Linux on G5 test. Without one, we still don't know for sure whether the bad performance is due to OS X or the hardware. And it's definitely useful for G5 owners to know whether they can expect Linux to improve server performance.querymc - Friday, June 3, 2005 - link
NT is not built on Mach. NT itself was originally a microkernel-based OS, derived from the design of DEC's VMS OS via the lead architect of both, Dave Cutler. It's currently very monolithic, a bit more than OS X because they stuffed a lot of userspace cruft from Windows 9X in the XP kernel for binary compatibility.Rick Rashid(sp?) was one of the co-developers of Mach, and he went to Microsoft, which is probably what OddTSI is referring to. I don't recall whether he went to research or the OS group, though. Either way, NT has no Mach code and does not share Mach's design.
Netopia - Friday, June 3, 2005 - link
OddTSI (Poster 37)-- Do you have any supporting data for saying that NT is built on Mach?Joe
AluminumStudios - Friday, June 3, 2005 - link
Intersting article. I wish you hadn't left out AfterEffects though because I use it heavily and I'd love to see a comparison between the Mac and x86 on it.OddTSi - Friday, June 3, 2005 - link
There's a semi-big error in your discussion on page 7. NT (and the subsequent Windows OSes based on it) is NOT a monolithic OS. In fact NT is BASED ON MACH. The main developer for the Mach micro-kernel was one of the lead developers of NT.octanelover - Friday, June 3, 2005 - link
I think it would be interesting, on the server side of things, to include Solaris 10 on Opteron in your benchmark list. Seeing as how Solaris is still a major player in the server world it would be nice to see how it fares along with Linux and Mac OSX.By the way, this article, IMHO, is darn near groundbreaking. Excellent work and very illuminating.
exdeath - Friday, June 3, 2005 - link
And before we talk about 10 Gb/sec busses, don't forget the Opteron can have like what 3 HT channels?And Hyper Transport specs allow for 22 GB/sec per channel (11 GB/sec bidirectional?)