Low-latency RAM takes less time to fetch the first bit of data after the CPU sends a column address strobe (CAS) signal to main memory. Such differences add up in tiny fractions of a second as your system processes instructions for the game you're playing or the database you're working with. Vendors list latencies for various memory functions; the first number is the CAS latency (CL), and when it's down to 2 on Intel-based systems (2.5 with AMD CPUs), you're really humming. Such memory carries a high price premium, often 20 to 40 percent more than slower RAM. A 512MB DDR400 module from Crucial, for example, costs about $100 at CL3 and $139 at CL2.
Vendors are careful to downplay any speed advantages. Latency differences may give you only a 2 percent boost in system performance, says John Stroozas, Crucial's director of engineering.
To gauge the benefits, PC World tested a PC with an AMD Athlon 64 CPU and standard memory, and then we swapped in faster RAM from Corsair Memory, Crucial Technology, and Kingston Technology, in turn. Improvement was negligible in most of our tests (see chart). Gaming tests showed the most benefit, with 4 to 5 percent gains in some cases. There was little difference among memory brands.
Low-latency RAM should eventually drop in price. But for now, if you didn't know what CAS was before reading this article, you probably don't need low-latency memory.
