Point of high speed ram?

[RockGuitarDude]

Ok I've been building comps for a while but I'm kind of self taught so I am unaware of some of the nitty gritty ram specs and what they really do.

Can someone please explain how timings (3-3-3 or whatever they are) and frequency affect actual performance. Also, what is the point of ram that is above DDR400? If boards only support up to DDR400 how do you use it? What is the real performance increase from the same processor going from PC-2100 to PC-2700 to PC-3200 to PC-3700 to PC-4000 and beyond?

Thanks to anyone who can help!

 

[Cerb]

The timings have a very minimal affect. Up to a KT333 board, I could feel the difference between 2-2-2-6 and 3-3-3-6. Not now.
For using faster RAM: RTFCM (Read the F---ing Chin-glesh manual). It's right there, as plain as, "for great happiness, best use AGP video card."
(some really are a trip)
The speed can help in games and other memory-stressing apps above the FSB. If you reach a given CPU's FSB bandwidth, gains beyond tend to be minimal (so dual-channel PC4400 won't do that much for a P4 with a stock speed FSB). Raising the FSB helps there.