DDR Ram speeds... 200/266/333 2100/2700/3200 What?!?! Confused

[misle]

I bought a motherboard, a Intel S845WD1-H. It will run with a 400 or 533MHz FSB. Ram specs are DDR 200/266 ECC SDRAM.

I also bought a Pentium 4 2.8 GHz with a 533 MHz FSB.

I searched on Crucial and found a match for the S845WD1-E (same base board, different options) board and it said that PC3200 is the highest they offer. So I bought it. I receive the RAM today and it says that the RAM is 400 MHz.

Is this a problem? If so, what RAM do I need?

Thanks for the help.

 

[vetteguy]

I'm by no means the memory expert here, but basically a P4's bus is "quad pumped" which means its effective operating freqency is 4x what its actual one is. So, a 533MHz fsb is really 133. DDR RAM is measured by 2x its actual, so DDR400 will operate up to 200MHz actual. If you're going to overclock, it's probably better to get RAM that has a higher bus rating so your memory doesn't become the limiting factor. Otherwise, you could go with PC2100 (which is 133MHz).

 

[Ilmater]

Originally posted by: vetteguy
I'm by no means the memory expert here, but basically a P4's bus is "quad pumped" which means its effective operating freqency is 4x what its actual one is. So, a 533MHz fsb is really 133. DDR RAM is measured by 2x its actual, so DDR400 will operate up to 200MHz actual. If you're going to overclock, it's probably better to get RAM that has a higher bus rating so your memory doesn't become the limiting factor. Otherwise, you could go with PC2100 (which is 133MHz).

That's dead-on. The actual front side bus speed on a 533MHz P4 is 133MHz, it just transfers 4x the data every clock, so it gets a 533MHz "effective" rating. DDR stands for Double Data Rate, and it sends twice the data every clock, so it gets a 266MHz "effective" rating at 133MHz actual.

 

[misle]

Oh! Thanks for clarifying that for me. Looks like I bought something a little faster than I needed, but oh well, it will work.

Thanks again.

 

[CraigRT]

You will only need a PC2100 DIMM to run in spec.
if you bought a regular 1.8A or something you'd only need to use PC1600 DDR memory. if you feel like running asynchronous to your FSB you may want PC2700 (333MHz)

hope this helps

 

[ElFenix]

just to be really confusing DDR ram is only DDR one way

async is probably a good idea with the P4s, though you'll get a little higher latency the P4 sucks down a lot of bandwidth (more than the PC3200 can provide, in fact)