HyperTransport and Opteron/Athlon64 Overclocking
The first question many will have about our efforts to look at how Athlon64 will perform is how we can possibly compare an overclocked Opteron to a chip that is not overclocked. In the case of the Opteron, the comparison is more accurate than you might first think.In normal setups (e.g. Athlon/P4), the CPU gets its clock from the FSB clock and multiplies it by the “clock multiplier” to determine how fast its internal clock should be. With a 16x multiplier, when the external clock ticks once, the CPU ticks 16 times. However, with the Athlon 64/Opteron, there is no FSB, so the CPU must get its clock from somewhere. It doesn't produce it internally; instead, it derives it from the native HT (HyperTransport) frequency, which is 200MHz, but because of the bus' nature, it runs at an effective 800MHz.
So, for our 1.8GHz Opteron 144, the multiplier is 9x, which is why raising the HT frequency to 222MHz increases the clock speed to around 2GHz. But we are increasing the HyperTransport clock in our overclocking, and not a FSB clock, which does not exist on Opteron/Athlon64. In real terms, this means our CPU overclocking has a significant impact on Performance, but it is unlikely that our increase in memory speed will have nearly as much impact on performance. Since we are nowhere near saturating the Hypertransport bus at 200 (effective 800), increasing HyperTransport to 222 (888) will not likely have much, if any, impact on overall performance. Our performance improvements, with Opteron/Athlon64, are mainly coming from increase in CPU clock — much more so than on the Pentium 4 or Athlon architectures.
Obviously, the PCI bus operates at a different frequency than the HT bus than the CPU, but they all operate based on multiples of each other, and are all derived from the HyperTransport clock.
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Anonymous User - Thursday, September 4, 2003 - link
I thought that the Athlon64 did not have the integrated memory controller. That's the big difference between the Opteron and the Atlon64, in single processor quantities.Wesley Fink - Thursday, September 4, 2003 - link
The latest runors at the Inquirer and Xbit Labs have the Athlon64 FX launching at 2.2GHz, which seems to be the rumor consensus :-) I have an Asus SK8N board I am testing now with an Opteron, and it supports both ECC and non-ECC memory - but it appears it MUST be fed Registered memory. This means regular unbuffered memory will not likely work on the Opteron based CPU's.Anonymous User - Thursday, September 4, 2003 - link
Interesting. And isnt the Athlon64 FX supposed to be running at 2.3 ghz? Add in support for Non ECC memory (which is slower) and color me interested.And here I was all set on buying a new 3.0ghz P4 system in a couple of weeks... <sigh>
WheelsCSM - Thursday, September 4, 2003 - link
Looks pretty good, how much are these things supposed to cost?sandorski - Thursday, September 4, 2003 - link
Sounds good! Hopefully the Athlon 64 *will* perform in a similar manner.Anonymous User - Thursday, September 4, 2003 - link
Oh, nevermind. Disregard #3. I understand what you're saying now.Anonymous User - Thursday, September 4, 2003 - link
"Our reference board includes full support for Dual-Channel DDR ECC memory, and the Athlon64 version will also support non-ECC memory"When it says "Athlon64" here is it referring to Athlon64 FX (Socket 940)? I thought that Athlon64 FX is basically an Opteron. And Opteron requires registered DIMMs with ECC.
Anonymous User - Thursday, September 4, 2003 - link
Awesome preview Wes, i can't wait to get one of these bad boys to play with after the 23rd, hopefully in the prommie!!keep up the good work.
Tony
(bigtoe)
AgaBooga - Thursday, September 4, 2003 - link
I wonder when Intel will respond to these articles on Athlon 64 with some Prescott previews