Hey, i've been putting together a design for my new system and i've been struggling to understand one thing about ram speeds. As i understand it, it's best to match your ram speed to your fsb. So a Conroe E6600 2.6Ghz, which natively has an fsb of 266Mhz (x10 multiplier), works in sync with DDR2-566. Overclock the E6600 to 333Mhz fsb for 3.3Ghz, and use DDR2-667. Overclock the E6600 to 400Mhz fsb for 4.0Ghz (and have a fire extinguisher handy), and use DDR2-800. So, it's pretty difficult to actually get a 1:1 ratio with DDR2-800, with any processor, given you need a 400mhz fsb, yet it seems to be a fairly common speed people buy. How is it that i read benchmarks and reviews showing performance increases with DDR2-800, or higher infact, when a systems only running a 266-333 fsb? I would have thought the fsb bottlenecks the ram, and thus it'd be impossible to actually get any benefit? I'm guessing the ram slows itself down to match the fsb, so could these performance increases just be coming from reduced latencies inside the ram? And then i see ram speeds at crazy values like 1066, or 1250 Mhz, can you even get any benefit from these? or is it just marketing? I get the feeling theres something i'm missing here, can anybody explain this to me?

This is because the way that your FSB is calculated.

The actual speed is what ever your CPU says it is, for example 266mhz. Now whenever data is sent over the FSB it sends multiple amounts of data for every clock cycle, for example 4 sets of data. So for this example a FSB that is 266mhz with 4x data is a 1066mhz bus. This is the same as having a FSB that sends 1 set of data for every cycle on a 1066mhz FSB.

I don't think any modern system uses a 1:1 ratio, most are more like a 1:4 or something similar.

I could have ratio 1:1. Any high speed memory could be set to work on lower speeds. So DDR2-800 could be set to work as DDR2-666 (aka 333 chip clock, which works 1:1 to FSB 1333 CPU aka 4x333)

Of course higher speeds increase throughput, ratio 1:1 is ideal for low latency (Actually ratios 2:1, and 4:1 would work nicely as well.).