AMD's Quad FX: Technically Quad Core
by Anand Lal Shimpi on November 30, 2006 1:16 PM EST- Posted in
- CPUs
Four cores, 1 Socket or Four cores, 2 Sockets?
One of the major arguments in favor of AMD's Quad FX architecture is the fact that you should get better performance scaling when going from 2 to 4 cores since there's no FSB limiting the data coming in to the CPUs. We looked at the performance scaling from a single FX-74 to two FX-74 processors in our Quad FX platform and compared it to Intel's Core 2 running at 2.66GHz with two and four cores enabled.
| Benchmark | AMD Scaling (2 to 4 cores) | Intel Scaling (2 to 4 cores) |
| 3dsmax 8 | 64.7% | 77.0% |
| Cinebench | 75.6% | 70.8% |
| DivX 6.4 | 29.5% | 35.0% |
| WME9 | 53.2% | 54.8% |
| Blu-ray + Cinebench | 147% | 135% |
| Blu-ray + DivX | 43.9% | 48.3% |
| Blu-ray + WME | 65.4% | 73.4% |
| Blu-ray + 3dsmax 8 | 63.1% | 77.0% |
| Valve Particle Systems | 48.8% | 93.1% |
| Valve Map Compilation | 42.0% | 44.3% |
Even when we take into account our heavy multitasking Blu-ray playback scenarios (which we will describe later), AMD's Quad FX doesn't scale any better than Intel's quad-core solution. All things being equal, AMD should have better scaling, however AMD's cores are inherently slower in most of these benchmarks and thus simply adding more of them is not going to make up for the deficit seen by one.
AMD will have better scaling on paper, but Intel has the superior micro-architecture today, which results in better performance and in most cases, better scaling than AMD. The same might not be true in the enterprise market, but we'll have to save that for a look at Opteron vs. Xeon.
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Viditor - Thursday, November 30, 2006 - link
If they can...
The 680a chipset has a direct HT link to each MCP, the 680i obviously can't do that and must bridge through the SPP.
Now if only we could find a review that actually showed that...;)
Seriously, the one major benefit of Quad FX is that it can run 4 GPUs. While I appreciate all of the conjecture and speculation, it isn't really a test of the facts, is it?
defter - Friday, December 1, 2006 - link
<quote>Seriously, the one major benefit of Quad FX is that it can run 4 GPUs.</quote>How that's a benefit? You can have 8 GPUs in a same system (AMD or Intel based, it doesn't matter) with a couple of NVIDIA Quadro Plex 1000 Model II's if money isn't an issue:
http://www.nvidia.com/page/quadroplex_comparison_c...">http://www.nvidia.com/page/quadroplex_comparison_c...
JarredWalton - Friday, December 1, 2006 - link
Fact: Quad SLI (7950 GX2) works on 590 SLI and 680i.Fact: Quad SLI (8800 GTX) does not exist.
Until the second item changes, we only have the first to go on, which is that current quad SLI works - at least as much as it works anywhere - on both platforms. And the QSLI drivers are still largely broken - you can run benchmarks, but as soon as you start playing lots of games rather than just benching, problems crop up. Neverwinter Nights 2 for example doesn't even run properly with CrossFire or SLI, so let's not even worry about getting QSLI support for now.
JackPack - Thursday, November 30, 2006 - link
8800 GTX requies two slots, which means it won't fit in the 4x4 motherboard. Quad-SLI performance has already shown to be poor using two 7950 GX2 cards. Finally, how do you bridge four 8800 cards together?Viditor - Thursday, November 30, 2006 - link
Huh?
http://www.bit-tech.net/hardware/2006/11/08/nvidia...">Single slot 8800 GTX
This is only when using a single MCP, the 680a uses dual MCPs.
The 680i uses one MCP and one SPP.
By having 2 sets of bridges (one bridge per MCP).
JarredWalton - Friday, December 1, 2006 - link
Quad SLI has problems whether or not you have dual MCPs. It's driver and software related - basically the drivers don't do AFR on a lot of titles and so you end up with lower than 7900 GTX SLI performance.As for two slots, they're talking the width of the cards. They only plug into one slot, but they fill the adjacent slot. Quad 8800 GTX would require eight expansion slots right now. Given that Vista 8800 drivers aren't even out yet, I think NVIDIA has other things to do before they worry about moving beyond SLI'ed 8800 cards.
PrinceGaz - Thursday, November 30, 2006 - link
I suppose you could replace the HSF with something smaller which would fit in a single-slot, which would have to mean water-cooling.Quad-SLI performance (or lack of) is probably a driver-issue.
Don't 8800 cards have two SLI sockets therefore allowing you to chain together as many as you like (in theory)?
casket - Thursday, November 30, 2006 - link
It appears with win-xp sp2... this quad fx stinks. How about Win 2003 or Vista Ultimate? It might change things drastically.Neosis - Thursday, November 30, 2006 - link
I don't think the problems in the benchmarks are not an opperating system issue. Two processors having totally four cores are not the same as a processor having the same number of cores. Additional latencies will slow down the performance.Viditor - Thursday, November 30, 2006 - link
Actually, they probably are...Windows XP is not NUMA aware, while Vista is.
In this case there is no difference...the Kentsfield has exactly the same latency as a 2 socket dual core because the 2 dual cores on-board don't talk directly with each other.