Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!
Because the memory controller on A64 systems is right on the CPU. This means that memory bandwidth will increase/decrease with overall CPU speed, regardless of how fast the actual memory modules are running. For example running the CPU at 240x10 with memory at 200 MHz (5/6 divider) will yield a higher bandwidth than CPU at 230x10 with memory at 230 MHz (1:1). Don't believe it? Try it.Guzuta said:Anyone else notice that bandwidth reading in Memtest changes with the CPU multiplier? For example, with the exact same memory timings, if I run FSB x 10 or FSB x 11, I get different bandwidth scores...why would this affect memory at all?
eric003 said:what about differences in memory bandwith with the same end cpu speed just diff multipliers and HTT speeds.
for example: 270x10=2700 VS 300x9=2700 ???
This I understand without any confusion... as this is a fundamental concept of overclocking..jivetrky said:Your RAM runs at the same speed of the HTT (if it's running on a 1:1 ratio divider)
This I also understand. cause increasing the HTT will increase the END cpu frequency (when multiplier kept same).jivetrky said:A higher HTT will make your RAM run faster. So if the HTT is set at a speed that your RAM can run with then that's good as you'll have more memory bandwidth. But if your HTT is higher than the rams max speed, then you'll have to use a divider to lower the RAM speed to something it can handle.
I'm cool with this too, The memory controller runs at the speed of the cpu (end Frequency)tebore said:The multiplier will affect how much bandwidth you get. As I stated CPU speed affects bandwidth because the actual memory controller is the CPU and it runs at the same speed at the CPU. There's no such thing as 1:1 on the A64.
umm, obviously because the max multiplier test run has a much greater end cpu speed then when you do a slower mutliplier.. for example 200x10=2000 > 200x5=1000tebore said:Do a simple experiment. Try same HTT speed, Try the max mult, then a slower mult. You'll see the lowered bandwidth with the slower mult.
The bandwidth should be very close, and I believe it will depend on one other factor which you haven't mentioned: total Hypertransport speed, i.e. HTT x HTT multi. My thinking is that whichever case has the higher Hypertransport speed will have the higher bandwidth (they can't be the same for both cases based on the numbers you've chosen).eric003 said:Given 2 different test cases: (any info or settings that I dont mention, assume to be held constant for both test cases, i.e. they are the same for both test cases)
Test case 1: 337 HTT x 8 (multi) =2700mhz (cpu speed)
Ram runs on divider, ram is running at 250
Test case 2: 270 HTT x 10 (multi) =2700mhz (cpu speed)
Ram runs on divider, ram set to run at 250
THE QUESTION IS: which test case has the greater memory bandwith... or do they have the same memory bandwith????????
Actually this scenario is not exactly possible. Here's why:eric003 said:MY SOLE QUESTION is this:
Given 2 different test cases: (any info or settings that I dont mention, assume to be held constant for both test cases, i.e. they are the same for both test cases)
Test case 1: 337 HTT x 8 (multi) =2700mhz (cpu speed)
Ram runs on divider, ram is running at 250
Test case 2: 270 HTT x 10 (multi) =2700mhz (cpu speed)
Ram runs on divider, ram set to run at 250
SOOO, the speed of the ram in both cases is running at the SAME speed. the end cpu speed is ALSO the SAME, therefore because the memory controller runs at the same speed of the cpu, 1:1, I am assuming that the memory controller in each of these test cases runs at the SAME speed.
THE QUESTION IS: which test case has the greater memory bandwith... or do they have the same memory bandwith????????
Tebore said:The multiplier will affect how much bandwidth you get. As I stated CPU speed affects bandwidth because the actual memory controller is the CPU and it runs at the same speed at the CPU. There's no such thing as 1:1 on the A64.
Do a simple experiment. Try same HTT speed, Try the max mult, then a slower mult. You'll see the lowered bandwidth with the slower mult.
jivetrky, I think you're getting memory "bandwidth" confused with memory "frequency". The memory bandwidth is the rate of data throughput to the memory (MB/sec), and on A64 systems this depends primarily on overall CPU speed, regardless of how the memory clock frequency is derived. For example, running 240x10 with memory at 200 MHz will yield a much higher memory bandwidth than running say 220x10 with memory at 220 MHz.jivetrky said:From all the information that I can find (and I'll admit that I can't seem to full grasp it) if you have your RAM ratio set to 1:1 (or set to ddr400 or 200mhz) in the BIOS, then changing the CPU multi will not change the mem bandwidth.
The pickey I posted was to show that the hypothesis that "At the same CPU speed and the same memory speed, multipliers and dividers have little or no effect, at least on Superpi".jivetrky said:well actually what would prove or disprove this is to run your HTT at 200 with both tests and just increase your multiplier and nothing else. And run a couple memory benchmarks (like sandra or STREAM) not superpi, which is affected much more by CPU speeds than the others.
EDIT: by changing your HTT you are changing the internal dividers between the CPU and ram. (according to the chart I posted earlier) So, since you have an FX chip, you can just change the multipier and keep everythign else the same. (which is what this thread is supposed to be about)