CL is an abbreviation for CAS Latency, an indicator of memory, the value after CL represents the time (in clock cycles) needed from the time the memory controller (memory controller) sends out a request to read the contents of a cell in the memory to the time it takes for the data to actually be sent to the output pin. So the shorter the value, the better. CL9 means that it takes 9 clock cycles from the time the controller sends out the command to receive the data. CL9 memory is the mainstream of today's third-generation desktop computer memory (DDR3).