I have a ram set all of which are PC2100 (its an old computer). Recently I was planning to upgrade my processor to a P4 3ghz FSB 800. But someone told me that using this with that kind of ram would severly underclock its speed and may not even work depending on my motherboard.

Well this is my motherboard http://www.asrock.com/mb/overview.asp?Model=p4v88
Will using an FSB 800 with pc2100 ram just result in its underclocking or will it not work at all? If its just underclocking will it perform as well an equivalent p4 but at FSB 533? or worse?

It would use a really low ratio but I can't see the performance being any worse if it's the RAM you're already using. The motherboard you listed will support this RAM.

thanks, so if i upgrade to a p4 fsb 800 while keeping my ram (pc2100) then it'll still run, although at a low ratio, right?
but what about if i buy a p4 fsb 533, which will now perform better (still with the same pc2100ram) the p4 with the fsb800 or fsb 533?

Theoretically, the RAM will run at the same frequency for either, namely 133MHz or DDR-266. It will do this by using a different ratio again between FSB and it's speed.

Overall the 800MHz FSB CPU will perform better than the 533MHz as it can communicate with the other components more quickly (except the RAM obviously), although the difference won't be as marked as a faster CPU or RAM.

Thanks. I'll get the FSB 800 then.

How much are you paying for the upgrade? You can probably get a C2D, new P35 mobo, and 2 Gig DDR2 for only marginally more money and more than double the performance.

Thanks for the interest. But I'm only planning on buying the processor and nothing else. So i doubt the money i'll use to buy it could afford all those. Besides my old system is an AGP, if i upgraded to a new mobo i'll have to buy a new GPU as well I just want to be able to play a few new games even at low settings, and made a lot of the old games at higher settings. I'm planning to build a new computer in about 3 years when i graduate from law, but till then just have to push this old one for when i actually have time to play.

I understand that but if I were you I would see if I could get some PC3200 to match it. It is not that expensive now. You can get 2GB for cheap on Ebay. Hell I got a P4 EE 3.4GHz for my old system for $150 bucks compared to the original $1500 dollars.

But the memory will run at 133 x 4 so your FSB for the memory should be 533 but getting some PC3200 will improve the performance of that CPU greatly.