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I came across this and I had always thought that the x2 and dualy opterons were very very similar--people always say, 'opterons are the chosen chips because they are more stable for servers etc etc'. I'm wondering if anyone has anything to add to this. Such as, is this info correct for say Opteron 165 Dual core vs. X2 4400? Which do you think is more important, the memory controller in opterons?

anyway, enjoy: (from custompc)

Since the introduction of the AMD64 architecture, AMD has taken a rather different approach to multiprocessing than Intel, which mostly revolves around the Hyper-Transport bus. This bus is one area that distinguishes Opteron processors from Athlon 64 CPUs, and the different Opteron versions from each other. All Opterons have three Hyper-Transport buses, whereas the Athlon 64 has only one. However, the way that these Hyper-Transport buses are configured varies across the three Opteron ranges. The key word here is 'coherent'. A coherent Hyper-Transport link allows the communication of cache-coherency information, whereas a non-coherent one doesn't. So a coherent link allows one core to pass requests to another core's cache and memory controller.

This is only important in a symmetrical multiprocessing (SMP) setup, which obviously isn't an issue with the single-core Athlon 64 or Opterons not meant for multiprocessing. For this reason, the 1-series of Opterons has three non-coherent Hyper-Transport buses, which is why you can't use two of them in a dual-processor motherboard. The 2-series, meanwhile, has one coherent bus to talk to another processor in a dual-processor configuration, and the 8-series has three coherent links, although only two are required in a four-way system.

However, the two cores in an Athlon 64 X2 CPU don't use Hyper-Transport to talk to each other. Instead, they talk directly to the on-die System Request Queue, meaning that any exchange of information between them goes at the core's full clock speed. Plus, while each core has its own cache, coherency information can also be transferred across the System Request Queue, so data can be taken from the other core's cache if found there.

A multiprocessor Opteron system's use of Hyper-Transport for communicating between the two CPUs actually makes the PC slower than an X2-based system, which explains why the X2 can achieve faster performance in some multithreaded tasks than a dual Opteron with the same core clock speeds. The X2 also performs very well in single-threaded tasks compared with single-core Athlon 64s, matching or even exceeding a single-core processor at the same clock speed. Intel's Pentium D, in contrast, has a greater overhead from managing the two cores, and tends to be slower than an identically clocked single-core CPU with single-threaded apps.

However, the X2 also has a drawback, in that it has only one
memory controller, which limits the memory bandwidth to 6.4GB/sec. With dual Opteron systems, each processor has its own controller, so if you install dual-channel memory banks alongside each processor, the two controllers can be run in parallel across the Hyper-Transport link between them, giving a theoretical maximum memory bandwidth of 12.8MB/sec. AMD realises this limitation, and will be launching a new 940-pin Socket M2 for Athlon 64 CPUs in 2006, which will support DDR2 memory. The new Socket M2 won't be the same configuration as Socket 940, however. As the memory controller is on the processor itself, a new line of Athlon 64 CPUs with on-board DDR2 memory controllers will have to accompany the new socket. Meanwhile, a 1,207-pin Socket F for Opterons is also due in 2006, although specific details about the socket are sketchy.

 

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From my understanding, I think they are comparing a true dual cpu setup vs. a Dual Core setup.

It's pretty much explaining how the opteron (socket 940) in a dual cpu application compares to a x2 dual CORE cpu.

I DONT think its comparing comparing a dual core skt 939 opteron to an X2 A64.
 

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Quote:


Originally Posted by n19htmare

From my understanding, I think they are comparing a true dual cpu setup vs. a Dual Core setup.

It's pretty much explaining how the opteron (socket 940) in a dual cpu application compares to a x2 dual CORE cpu.

I DONT think its comparing comparing a dual core skt 939 opteron to an X2 A64.

I second that and was just about to write the same thing. Read carefully what it states about the ram configuration and you can see that it mentions having ram slots for each processor. What's the date on that article? I'd be willing to bet it's before Opterons even came out on socket 939.
 

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Quote:


Originally Posted by sccr64472

I second that and was just about to write the same thing. Read carefully what it states about the ram configuration and you can see that it mentions having ram slots for each processor.

seperate memory controller is a straight give away


Skt 940 opterons = cheap

everything else not so cheap
 
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