A question of CAS

[iceliquid]

What does CAS2 and CAS3 mean? and how do they really differ?

And what are the implications of running a stick of pc100 cas2 and a stick of pc133 cas3?

Just curious since my friend bought this up recently.

 

[pm]

CAS => Column Address Strobe

It refers to the number of cycles that need to occur between sending the first part of the address to the memory chip and then sending the second part. It's measured in clock cycles - so CAS3 memory requires 3 cycles delay while CAS 2 requires two. Performance-wise, running with CAS2 memory will enable a system-level speedup of approx. 3-5% over CAS3- although in certain apps (RC5) you will see virtually no speedup and in others (DiVX encoding) you will see more like 8%.

Running CAS2 memory with CAS3 in automatic mode (ie. the settings are read from the SPD contained on the memory DIMM) will have the effect of running both memory sticks at the slower speed (CAS3). If you override the settings and run both sticks at CAS2 then you are effectively overclocking the CAS3 memory.

 

[iceliquid]

pm, U R DA MAN!

Thanks!

 

[Kingofcomputer]

from crucial faq:


What is the performance difference between CL2 and CL3?


Description:

What is the performance difference between CL2 and CL3?

Solution:

CL2 parts process data a little quicker than CL3 parts in that you have to wait one less clock cycle for the initial data. However, after the first piece of data is processed, the rest of the data is processed at equal speeds. Latency only affects the initial burst of data. Once data starts flowing, there is no effect. Bear in mind, a clock cycle for a PC100 module is 10 nanoseconds so you probably won't notice a significant performance difference. Most systems will accept either latency part. However, there are some systems that require either CL2 or CL3 parts. These requirements are built into our Memory Selector?.