CAS latency is a memory timing parameter that helps determine the potential bandwidth of a PC, ie. potential processing speed in mb/sec.

My bios allows the timings to be set manually (most do) either induvidually, or as a preset mode, ie. "Turbo RAM timings".  In my "turbo" mode, the memory timings are set to take advantage of very fast, high quality RAM modules, with a CAS Latency of 2.0 (nanoseconds?). The higher the CAS number, the slower the memory timing.

It's basically a bios tweak to get the most out of your system. If the RAM won't handle the fast timings, it will usually lock up or crash the system, and because the setting was placed in BIOS, the PC may not boot until the BIOS is set to default using the "clear CMOS" jumper on the mainboard.

It's no big deal, and worth trying to see if the RAM works with fast timings, as long as you are confident in restoring your BIOS settings.

Silly me - it was there all along. ....