Articles :: How to Get the Most from Your Memory ::

Doc Overclock · 06-17-2002 · Category: Guides

SPD And CAS Latency Values

Every memory module has a limit that is predetermined at the factory. The type is usually marked on the module's label. The information is also stored inside a "SPD" chip, a small 6mm chip mounted on one corner of the memory module. You will see this as a setting option in the BIOS to determine your memory's speed automatically. CAS Latency is measured in CPU clock cycles with the lower number being the fastest and the highest being the slowest.

The CAS Latency value can usually be changed to the following settings: "1", "2", "2.5", or "3" depending on your available BIOS options.

If using different CAS latency memory in your configuration such as one chip being CAS 2 the other CAS 3 do not set the memory to the lower CAS 2 setting as this can cause stability errors.

The preferred setting choice is to have the BIOS use the SPD chip on the RAM module to determine CAS value. If this option exists in your BIOS for stability this setting should be used. Overclockers have pushed the limits of memory far beyond spec to achieve higher frequencies by altering these settings.


  1. Introduction
  2. SPD And CAS Latency Values
  3. The Memory Bus
  4. Bank Interleaving
  5. System Timing and Memory Speed