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does cpu speed determine RAM speed?

does anyone knwo if this is true? b/c i want to a 400mhz 512mb stick of RAM but someone told me that if ur cpu runs @ 266mhz then ur RAM can't go any higher than that. quick replies would be good. thanks


F@H - Is it in you?
Staff member
Political User
your cpu's front side bus you mean?

if thats what you are asking about then in a manner of speaking your overall systems performance and efficiency is determined to an extent by the front side bus of the cpu and the clock speed of the memory...

ideally you want to be able to run everything synched perfectly so neither the cpu nor the memory is the bottleneck on the other...

if you have ddr400 memory then you want an fsb of 200mhz (x2 coz its double data rate == 400) to synch perfectly and enable best performance..

your memory can run as fast as you want it to go within limits of course...

if you overclock your computer by dropping the multiplier of the cpu and upping the fsb (effectively getting the same clock speed or higher) you are likely to get a better performing rig... also if you up the clock speed of the memory you can synch it...

naturally the memory and the cpu and the motherboard have to be able to handle any overclocks you throw their way but it gives you an idea that the ram does not have to be limited per se...

however if you are kicking it higher it makes little sense to be doing it w/o synching things first off...
Lots of boards now are running Dual Channel mode on the RAM so your taking 800Mhz on a PC3200 DIMM. These speeds can be taken advantage of with newer CPU's which run at a higher FSB.

I myself have been drooling at a nice set of dual 512mb DIMMS of PC3200 with a CAS around 2.5 and heatsinks on. Still is rather expensive though, for the price of buying that I could get a new motherboard that supports a 64-bit processor and a new CPU!

Example of ‘syncing’ using a AMD 2100+ XP CPU:

Stock Speed 13x133MHz = 1729MHz

Overclocking CPU to avoid bottleneck, extra cooling may be required
CPU 9x200MHz = 1800MHz
RAM PC3200@2x200MHz = 400MHz

Underclocking CPU to avoid bottleneck
CPU 8x200MHz = 1600
RAM PC3200@2x200MHz = 400MHz

In either case taking full advantage of the RAM’s speeds, you could overclock the RAM itself if its good stuff (low CAS rating) but you’d probably want to watch those temperatures.
With an NF7 motherboard, 266 mhz FSB and 2 sticks of RAM at 266mhz there is no point in going 400 mhz RAM. No noticeable improvement.

Better to do what Sazar suggested and see how much you can overclock the fsb and ram running them at the same speed. Make sure the PCI and AGP clocks stay at 133 though.

The NF boards effectively double the ram speed by accessing the 2 sticks sequentially so you get close to 533 effective ram speed with 266 mhz ram. Going to 400 does no good because the 266 cpu FSB is choking your overall system performance.

I'm running my xp2500 at 2800 with my 333 ram overclocked synchrounously with it 183/366. Gave a me nice little boost for free.
no i threw out one of my 256 sticks so i only have one left now...im thinking about selling the remaining one and just geting a big fast 512 stick. anotehr question i have is whats the best affordable RAM to get??? i heard crucial was alright and they also give life time warrantys but im afraid they might not work as well with AMD then other brands like kingston?
Crucial, Mushkin, Kingston, and Samsung are all good, affordable brands to get. Just avoid words that make them sound cheaper like "Value" or "Hobo Series". It's worth the extra few dollars for higher-grade RAM.

Son Goku

No lover of dogma
I've used Corsair XMS of late and haven't had any problems with it.

To expand on what Sazar mentioned...the CPU's clock is determined by both the front side bus (which is the clock the RAM runs at), multiplied by the multiplier. So in this respect memory clock can effect CPU clock... If the fsb is a lower clock then the CPU was meant to run on, then the CPU will clock lower unless the multiplier is increased.

I had this happen with my current system when I first got the mobo. For whatever reason, with an AXP 1900+, and DDR 300 MHz RAM (Corsair XMS 2400 CAS 2.0), the board (Asus A7N266-E) would auto-detect it as DDR 200 RAM (100 MHz x2 for DDR) and ran the CPU at 1.2 GHz instead of 1.6... For me, there was an easy fix...set it to manual, and bump up the clock to where it should have been. Latter BIOS revs on my board didn't have that prob though.
I've only ever used Geil with AMD chips. I've seen one bad stick, and I think it was because dumba*s I built the system for added heatsinks to the ram and I think he was over-generous with the adhesive.

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