Explain the relationship

[gerwen]

Bear with me for a min. I'm currently looking at going with a c2d for an upgrade. I've been poking around looking for best price vs performance. C2d is the obvious choice.

Before coming to the forums here, my mainboard choice was between the Gigabyte S3 board, and the Foxconn P9657AA-8KS2H. After reading down to about page 5 here, it looks like the Gigabyte is the way to go.

I'm now just looking at RAM and Processor. I need some help to make choices. Like I said, i've been reading here for the last few hours, and gained a pile of insight. There's some basic knowledge i just haven't found here yet.



How are the FSB, the Cpu multiplier, memory speed, and memory timings related?

I understand that the FSB x Cpu Mult is Final clock speed. ie 400FSB x 7 Mult (E6300) = 2.8GHz.
How does the memory speed come into play? Does it have to be a multiple of the FSB, or is it set independently of the FSB?

I've read many times that the higher you push FSB, the faster your memory has to run, but how are they related?

Then there's also the 4-4-4-12 type timings. I expect that these are related to how many clock cycles it takes ram to do certain things, so lower is better performing, but more demanding on the chips. So they can be adjusted upwards, to sort of slow them down and perhaps allow the Ram to be run at a higher clock speed?


Thanks for any help you can provide.

 

[40sTheme]

Well, i'm not too sure about FSB/Mem speeds, but timings are the amount of time it takes for the computer to acess something in the RAM. 4 = 4 milliseconds.

 

[n7]

RAM runs syncronously to the FSB by default. Or 1:1

Say you have your E6300 @ 7x400 (2800 MHz).

That means you need RAM to run @ 400 MHz aka DDR2-800.

It can also run faster though, such as 4;5, or 2:3.

And yes timings can be loosened to achieve higher frequencies.

 

[orion23]

Originally posted by: n7
RAM runs syncronously to the FSB by default. Or 1:1

Say you have your E6300 @ 7x400 (2800 MHz).

That means you need RAM to run @ 400 MHz aka DDR2-800.

It can also run faster though, such as 4;5, or 2:3.

And yes timings can be loosened to achieve higher frequencies.

Correct, but RAM can also run faster or lower than the FSB by using a "devider"

Most people I know like to use the 1:1 ratio.

Others (if the memory allows it) like to run the RAM at the highest possible)

And some if forced (slow RAM) will run a devider so that the RAM runs behind the FSB (slower performance)

Reason why it is recommended to always get faster RAM in case you might want to push the FSB sky high. Good DDR2 800mhz such as the GSKill 2GBHZ 4-4-4-12 (overclockable to 1000 speeds) should do the trick.

Or get DDR2 1000mhz

 

[Furen]

The FSB clock is the base clock from where the other clocks are derived (in AMD's case, the HTT is the base clock, since the FSB in integrated into the die).

The CPU multiplier is just that, it multiplies the base clock in order to get the CPU clock speed (ex. a 266MHz FSB with a x7 multiplier gives you a 1.86GHz clock speed).

The Memory clock, too, is also derived from this base clock. In Intel CPUs there's a FSBRAM ratio. For example, if you are running DDR2 533 on a 266MHz FSB then you are running with a 1:1 ratio (since DDR clock speeds are doubled, the real clock for the memory is actually 266MHz). In this case, every time you increase the FSB you'll have an equivalent increase in DRAM clock. If you run at DDR2 800 on a 266MHz FSB, on the other hand, you are running a 2:3 ratio, so for every two MHz of FSB you get 3 MHz in DRAM clock. At the other side of the spectrum, running DDR2 400 sets a 4:3 ratio, which means that for every 4 MHz in FSB you get 3 MHZ for your DRAM clock.

Timings are not directly tied to the clock speed but rather to the memory chips' specific clock abilities. For the most part, the higher your DRAM clock the looser (as in higher numbers) your timings will have to be (so if you're hitting a ram-clocking wall loosening your timings can help) but there's some memory that can do DDR2 1100 at 5-5-5 while other RAM cannot reach DDR2 800 even with those timings.

 

[gerwen]

Thanks for the info. It's starting to get clearer now.

So, if i go with the gigabyte S3, and some 667 ram, i shouldn't have problems hitting a 333Mhz fsb for 2.3 Gig on the E6300 or 2.67 Gig on the E6400. That's assuming the mobo stays stable at those fsb's, but the memory shouldn't be the limiting factor.

If i get 667 ram with CAS3 or CAS4 timing, there may be room to change the timings down to CAS4 or 5, and push the bandwidth up a bit, and maybe hit a 400FSB? (Does the S3 mobo allow you to do this?)

I'm only getting 1GB of ram, and trying to stay cheap. I can't order from newegg, as i'm in Canada, and they don't ship here. All the ram recommendations i read around here are for 1GB sticks.
Should I get a 1 gig stick, or find two 512's to get into dual channel mode?

Currently i'm looking at (Canadian funds):
Crucial Ballistix PC2-5300 1GB 2X512 DDR2-667 BL2KIT6464AA663 These are CAS3 - $183 (possibly on n7's list)
Mushkin EM2 PC2-5300 1GB 2X512MB DDR2-667 CL4-4-4-12 991379A - CAS4 obviously - $132
Centon Dual Channel 1024MB PC4200 DDR2 533MHz Memory (2 x 512MB) CAS4 -$140 (seems to be on n7's sig list)

Picking out overclockable memory is a daunting task. Can i save the headeache and pick up any brand of PC6400-800Mhz memory and be confident that i can hit 400Mhz FSB, at least as far as the memory is concerned?

thanks again