Why does my DDR400 run at 333mhz?

Hi,

I bought two sticks of DDR400 ram and a new motherboard that says it supports DDR400. I installed everything but the ram shows up as 333mhz.
When I run CPU-Z, it says my memory frequency is 167.5 mhz. Why is this happening?

My processor is a P4 2.4 ghz, 533FSB
Motherboard is GIGABYTE 81848P-G
Two sticks of DDR400 (PC3200)

Any ideas?

 

Hmmm... I could be wrong, but I don't think your motherboard will support RAM that fast, and underclocks it to use. I'd check your motherboards manual to confirm. I can't find this board on the gigabyte website.

 

I questioned that too, but I checked both the manual and the box, and they both say that the MB supports DDR400mhz.

Is it possible that the CPU dictates the RAM SPD? For example, since I am using a CPU with 533mhz FSB, does that limit my Ram to 333mhz?

PS the full part number for the MB is GA-81848P-G

 

What kind of ram is it?

I have 2gb of Corsair VS ram here that will not run at 333, unless I set it manually. It always clocks in at 333mhz when I set it on auto.

 

in your bios you should have the choice of setting the speed, manual or by speed.

 

Quick google shows that indeed your mobo can handle 3 X DDR 400 RAM:

http://www.computersolutionz.co.uk/group.asp?name=Motherboards

Okay when they say RAM SPD (Serial Presence Detect chip) this does not stand for speed but rather what the manufacturers define as safest RAM timings and MHz for that RAM. Just like CPUs' the RAM can go faster (up MHz) and at tighter or looser timings but are when set to SPD these are the manufacturers desired timings and speed to optimise stability.

Now your FSB is @533 MHz because you have and Intel that is quad pumped (four lots of data sent per cycle) you actual speed is 133MHz, refer to OC guide:

http://forums.majorgeeks.com/showthread.php?t=52812

Finally CPU-z says your RAM freq is 167.5MHz but because you have DDR (Double Data Rate) you are actually 2 X 167.5=~333MHz per cycle.

So I hope this has cleared up the figures for you. I believe that you have a DRAM:FSB ratio defined within your BIOS that maybe holding the RAM back or your RAM is set to SPD within your BIOS and this is what may hold the RAM back. You need to check your BIOS for DRAM Frequency (in Advanced Chipset Features). Start here and post what you find.

 

Okay I have done a little more maths and here is what "I think" is occuring, others please correct me!

As stated before your FSB is actually@133MHz X Multiplier = CPU GHz, you will get this on the first screen of CPU-z, can you post these figures?!?

Next if you look on the Memory tab of CPU-z and look at FSB: DRAM this is your RAM to FSB ratio. What I am guessing is that you have 133(FSB)/167.5(RAM)=~0.79 or basically 4:5 ratio and that you RAM is already running quicker than your FSB. The only way you will overcome this is to up your FSB and OC the CPU. I maybe wrong with this but the maths is adding up and you will be able to confirm it with CPU-z. Can you please post the results just to satisify my guestimating.