Ah fark. CPU - NorthBridge - Memory help
When you look at the specs of a stick of RAM, like say Corsair XMS 2700, and you see 333mhz, what EXACTLY is that in correlation to? Is that the speed between the NorthBridge and the module?
Also, if a Barton 2500+ is running at 333 FSB (Which it won't be for long
), will there be any increase in performance if the Memory is 3200 opposed to 2700 (400mhz vs 333mhz respectively)?
My reason for asking is that I had thought that an efficient AMD machine had matching speeds (333mhz, in the case of the 2500+ and XMS 2700). I had figured that if the memory was running at 400mhz, and the FSB was only at 333, that the difference between the CPU and Memory wouldn't matter, since the CPU could receive data at 400mhz, it'd end up being a waste of money (not like the difference between 3200 and 2700 memory is much). I believe this is partially correct and wrong, though I'd like some insight.
Also, if a Barton 2500+ is running at 333 FSB (Which it won't be for long
), will there be any increase in performance if the Memory is 3200 opposed to 2700 (400mhz vs 333mhz respectively)?My reason for asking is that I had thought that an efficient AMD machine had matching speeds (333mhz, in the case of the 2500+ and XMS 2700). I had figured that if the memory was running at 400mhz, and the FSB was only at 333, that the difference between the CPU and Memory wouldn't matter, since the CPU could receive data at 400mhz, it'd end up being a waste of money (not like the difference between 3200 and 2700 memory is much). I believe this is partially correct and wrong, though I'd like some insight.
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In this case, PC2700, running at 333 MHz DDR (166) offers 2.7 GB/sec memory bandwidth.
It's best to keep the memory bus (ie 333 MHz DDR) and the system bus (ie Athlon 2500 with 333 MHz FSB) in sync to get the best performance.
I believe Thrax has much more information regarding memory technology for the Athlon platform
Boards made two years ago typically could not do this, the exceptions were very high end boards and kinda more rare. But try with an UNDERCLOCKED CPU FSB and a RAM speed base set to normal RAM and see what happens, then try PC3200 if that works stably for 24 hours while folding-- expect a speed decrease in folding, it should not barf though if the board allows faster RAM base than CPU FSB settings.
A lot of newer BIOSs will let you set RAM base speed at various speeds separate from FSB. Way I discovered this on my board is that the RAM base and the FSb boht defaulted to 100 beofre flashing BIOS. After flashing BIOS, my DDR333\PC2700 was set to a 100 by default. I cranked it to 166 base, as RAM is double-pumped with DDR. And forgot to look at the FSB. Booted, ran for two days, noticed bogging, set FSB right AND pumped the RAM up about 10%. A week later, stable as heck. Mine is only an MSI KT4VL board.
So try safely before you buy RAM.
John.
Why here I am, like white on rice my little want-to-knowers.
DDR266:
133 * 2 * 8 = ~2100
8 is the width of the bus in bytes, as you may or may not know, the channel between the CPU and the memory for DDR is 64 bits. Eight bits per byte, so 64 / 8 = 8!
And so on...
166 * 2 * 8 = ~2700
You see, the Athlon bus is very efficient, but extremely narrow. It regularly achieves 98% memory efficiency, but it's not wide as per say, the Opteron, or the Pentium 4.
The FSB on the Athlon is the maximum amount of data the bus can accept at any given time.
If the CPU has a 333 FSB, the maximum performance will come from DDR333, DDR400 will oversaturate, and more often than not, slow the Athlon down. On DDR400, the signal timing is extremely rigid, and the slow Athlon bus is more likely to just skip a beat and drop data to wait for the next memory cycle.
DDR333 isn't AS tight, so it does offer some performance benefits on older 266 FSB Athlons.
Realistically, however. I would match every new AMD system with PC3200, as the SPD timings are TYPICALLY still DDR333, furthermore, they can be forced into DDR333 speeds with much tighter timings than any OOB PC2700 modules. The end result is a computer with awesome PC2700, great PC3200 for the future.
Oh, as to 8 bit pipe, um, how do you get an 8 chip 512 MB out of that width??? My RAM IS 8-bit width, but have seen single-side 8-chip 512's and the board is stated to take them. DDR333 and DDR400(NON-dual-channel).
John.
How far does a stick of XMS 2700 typically OC?
It's probably 64-bit high-density memory. Actually, AFAIK, every DDR SDRAM module is 64-bit as JEDEC specifies that the interface must be 64-bits wide. Even old SDR SDRAM is 64-bit in width.
Intel's DC-DDR controllers works exactly the same way, except the memory bus when operating in dual-channel mode is 128-bits wide (2 independent 64-bit channels operating in Lock Step mode, essentially doubling bandwidth across the bus).
Good low-latency XMS2700 will maybe hit PC3200 speeds. There's no guaruntees. It's anyone's guess after that, as it really depends on the memory chips utilized on the module.
So say with good latest RAM, 20%, older gen 10-15%. About average for a non-aggressively pinpoint cooled system. Trick would be to allow two-push or two-pull per cycle, and have not seen that stable without dual channleing, the traces will not take the load stably, you get random junk coming into NB. You CAN run DDR400 if you compensate with timings to underload it relative to its native abilities, but net result is PC3500 to PC3400 effective throughput equivalence. So, if you want to get DDR400 non-dual channel and reuse later, you can but will pay for the investment performance wise in boht old and new box and by getting nearer to cutting edge now and paying for it money-wise. Would not bother, would invest elsewhere.
John.