<div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Anyone else know about this multiple of 400MHz thing? I'll dig around<br>
the net now.<br>
</blockquote></div> <br>I am not sure how much the actual performance would be different but I believe I know the reasoning behind the 400 MHz clock. If you are using DDR2 800 (ie PC6400) RAM then ideally you would want the front side bus to be running at 400 MHz. Then the combined speed of a matched pair of DDR2 memory will be 2 x 400 = 800 MHz. If you have a processor that is not clocked to run at some multiple of 400 MHz then the front side bus won't be running at 400 MHz. For example I have a Core 2 Duo that comes factory clocked at 2.13 GHz. That comes from a 266 MHz FSB x 8 multiplier = 2.13 GHz. So to get each of my RAM modules to run at 400 MHz, the clock for the RAM is running at 3:2 ratio of the FSB, (266 x 3/2 = 399 MHz). Generally when your memory isn't running 1:1 with the FSB then your performance won't be quite as good. There weill be higher latency etc. This is generally an issue that overclockers deal with, trying to strike a balance between getting your FSB and processor as fast as possible and keeping your RAM 1:1 with the FSB. An ideal overclock for my Core 2 Duo would bump the FSB up to 400 MHz. Then the processor would be running at 8 x 400 = 3.2 GHz and the RAM would be running 1:1 at 2 x 400 = 800 MHz. <br>
<br>Generally with a given processor and RAM you will get better performance if your FSB and RAM are running 1:1. Keep in mind that you can overclock to get this for many of these processors. However, choosing one processor over another just because it runs on a 400 MHz FSB isn't necessarily going to give you better performance. It would be hard to say whether an extra 100 MHz or 200 MHz in processor speed will affect performance less than the clock ratio on your RAM being 1:1, without actually testing the systems out. It certainly wouldn't be one of my prime considerations when selecting a processor. <br>