View Full Version : Ram Frequency and FSB Compatibility

06-21-2005, 12:08 PM
Ok so I'm running a 2.0ghz p4 with a 400mhz fsb. I currently have 2 sticks of pny optima in the system. On the front of the box they say ddr333/266. Now they are running at 266mhz because of my fsb being at 400mhz and not 533. I know that if I had the 533 fsb then the ram would clock in at 333mhz. Now... I want to buy to new sticks of ddr400 ram because I am going to upgrade my cpu to a 3.0ghz 800mhz fsb in the future. Now the ram I want to buy doesn't say ddr400/333/266 but it does say "only compatible with ddr400 systems" and only says ddr400 on the front. My question is will this RAM be clocked down to 266mhz like my pc2700/ddr333 ram and work fine, or will it not register/not work/blow up my pc? Thanks for the help.

06-21-2005, 12:45 PM
You'll probably have to get a new board to support the CPU considering they're different sockets. You'll also have to make sure that the board you have supports DDR 3200 (400MHz) ram (which is most likely will). If you have both then yes, it will support your ram. Also, if you ram is running at 266MHz then that means your FSB is only running at 133MHz. Your FSB should be set to 166MHz to get the 333MHz from your ram. You still won't get 400MHz fsb from the cpu but it will give you a decent performance boost. Unless it's split 4 ways on the intel... In any case you still need to take your FSB up a notch.

Oh yeah, if you put the DDR400 in your slower computer it will just underclock it to the board speed. Although you should be able to get full speed with it if your CPU and board are running at 400Mhz. Unless your board just doesn't support it.

06-21-2005, 12:59 PM
Actually the FSB is 100, but the RAM frequency will be 133. Any DDR RAM, regardless of it saying "only compatible with ddr400 systems," will work at a lower speed, which is what it will run at.

06-22-2005, 04:52 AM
Ok thanks you guys... joe...you answered my question in the second paragraph. I just wanted to no if the RAM could be underclocked... My board does support 800mhz fsb and i want to get a new cpu that has a socket 478 like my current 2.0ghz. Also I now have a question. My manual for my mb says that according to the fsb memory will be clocked as follows. 400fsb=ddr266...533fsb=ddr333...and 800fsb=ddr400" I guess I'm wondering if my fsb is working at 400mhz when my ram is at ddr266. (I know that the fsb is actually 4x100mhz...that's how intel works) ALSO if I have 2 sticks of pc2700 and 2 sticks of pc3200 will both operate were they should be at or will the pc3200 have to clock down to conform to the lower speed ram (asuming I get my 800fsb cpu) wow I wrote a lot thatnks 4 the help.

06-22-2005, 05:15 AM
Yes, the FSB will be 100MHz x 4 if the RAM is at 266MHz DDR (133MHz x 2).

If you have multiple speed of RAM, they will all run at the speed of the slowest.

06-22-2005, 05:54 AM
There you go. If your sticks (either of the speeds) are 512, you will be better off using the fastest one running 1 gig instead of all 4 running slower at 2 gigs.

06-22-2005, 06:50 AM
ok thanks for the help