ok. lets say i had a mobo that said the ram type was 184 pin DDR 400 (PC3200). and i had a stick of ram that was 184 pin DDR 333 (PC2700). could i use this ram on this mobo? thanks -tom

You could but both memory modules will run at the lower speed of the PC2700 RAM. If you try to run it at the higher speed of the PC2300 RAM you will likely have a very unstable system. Stuart

Besides speed you should also take note of the cas latency. Both must be the same. For example, those rated at C3 will have cas latency 3 at 200MHz, 2.5 at 166MHz and 2 at 133 MHz, while those rated at 2 or 2.5 means the speed is always at 2 or 2.5 regardless of where the speed is at (133,166,200). For intel systems (using intel original board), you can mixed different speed/cas latency without any problems because it will shift to a speed where the cas latency are the same for all (eg in dual channel mode channel 1 running at 200MHz C2.5 whereas channel 2 at 166MHz C2.5). For AMD systems, you need to choose the ram speed/cas latency correctly or else you will get lockups/crashing.