I expect to buy a new motherboard soon (ASUS A7v266E)and 512M of pc2100 DDR SDRAM. I don't expect to overclock it. Is there a difference in gaming performance depending of memory type, (CL2, CL2.5, 2-2-2). Are they all running stable?
Manufacturers tests their memory to see at what settings can be achived. Modules sold as CL3 are those that could not run correctly at CL2. Usually there is a margin of error and some manufacturers are more conservative in their ratings than others. I built two systems will Crucial PC2100 CL 2.5 and both run stable at CL2.
CL 3 memory waits 3 cycles to begin a transfer While CL 2 waits 2. The bus is double pumped hence the 2.5 option. This only affects the begining of a trasfer, after that it is in burt mode with two transfers per clock cycle.
For most application there is only a 1% difference between CL2 and CL3. With games you can expect a 5% difference. But the important thing is that CL2 is higher in quality and hence more stable.
PC2100 is very stable. PC2700 is still a little buggy but new more stable modules will be available soon.
Just don't buy cheap ram, some people get lucky others end up with ustable systems. If you want quality you can't go wrong with Crucial or Corsair. Also people tend to have less problems with one larger modules as apposed to two smaller.
The onlything that will reduce the lifespan is overclocking/overvolting even then you system will likey crash before you reach the point at which your memory module is being damaged. The CAS setting only changes how long the chipset waits before reading the data from the output pins, the frequency and voltage remain unchanged. The memory is desined to continuously read per half clock once the transfer begins so not waiting an extra cycle is not going to affect it. The only way that setting your memory to CL2 will affect its lifespan is if you have to overvolt to get it to run stable.
BTW the lifespan for DIMMs is no less than 20 years, so even if you overclock and overvolt your equipment will be obsolete before it wears out.