CAS Latency question


Aug 2, 2002
Hey everyone,

What exactly does CAS Latency 2-3-3-6-T1 mean? How does it relate to CAS2.5 and CAS2.0? Does PC2700 come in CAS2.5 AND CAS2.0? What's the performance increase between the two? And sort of off topic, but for a 333MHz FSB motherboard/processor that most likely will not be overclocked, do you guys recommend getting PC3200 RAM at all or should I stick to PC2700?

Thanks in advance

Lord Evermore

Diamond Member
Oct 10, 1999
CAS Latency is only the first number, 2, 2.5 or 3. The next two numbers relate to RAS precharge and RAS to CAS Delay. The last number isn't always listed, depending on the brand. It's the RAS active to precharge. Some brands also list the command rate, usually 1T or 2T.

Lower numbers mean less latency for memory accesses. CAS Latency is the most important. You can find memory with ratings of 2-3-3-6, 2.5-3-3-6, 2-2-2-5, et cetera. You'll never see a module with a higher CAS Latency but lower ratings for the other numbers, like 2.5-2-2-5; CAS latency is always reduced first, then the others may be reduced with better modules.

All memory frequencies are available in a variety of latency ratings. A higher frequency is more important than a lower latency rating, up to a limit. With a 333MHz bus Athlon, the CPU won't be able to make any use of the bandwidth of PC3200 (400MHz), so getting anything higher than PC2700 is usually needless; running the frontside bus and memory at different speeds also introduces latency penalties due to the busses being out of synch.

You can get PC2700 with lower latency ratings for the same price or lower as PC3200 with higher latencies. You may however consider the prices and future usage, and get PC3200 that has decent latencies, and clock it at only PC2700 speeds with very low latencies. Then if you ever do need 400MHz memory, you'll be able to avoid buying entirely new modules.