Our module today, rated at CL 2.5, its one of Crucial's best selling ram upgrade options. DDR (double data rate) operates optimally at twice the speed of conventional SDRAM. This is accomplished by having the output of the ram activating on the rising and falling edges of the system clock. The rating of 2.5 is the CAS (Column Access Select) which is the amount of clock cycles it takes for the memory to respond to a command. And of course, the lower the number the faster it is.
FULL STORY @ GIDEONTECH (http://www.gideontech.com/reviews/cr_128ddr2100/)