RAM "CAS Latency" Question

[pjpjpjpj]

If you have two RAM modules and they have different CAS Latency, does that matter?

My server has (only) 512 Mb of RAM... upon reading here about the improvement that more RAM makes in extenders, I decided to add some. Turns out that I have two bays and only one full (I assumed I had 2x256, I only have 1x512). So I want to add another 512Mb. The existing 512Mb has a label and I know it is (yeah... old...) "DDR266/PC2100", but I don't think it mentions the CAS Latency.

I am looking on newegg.com and they have modules for nearly the same price, some with CAS latency=2, some with CAS latency=2.5. I know that lower is better, but if I buy the one with CAS=2, and the existing one is CAS=2.5, would it still work? And/or would there be adverse effects?

I know I should just buy two new 1Gb modules, but I'm a little tight right now (especially on the WAF for spending on Sage).

[MattHelm]

Originally Posted by pjpjpjpj

If you have two RAM modules and they have different CAS Latency, does that matter?

Does CAS matter, it depends. ;-)

RAM has 2 (really about 10) things that matter on how "fast" they are. I'll try to explain it simply.

There is the "clock" speed of RAM. This is the clock that is used to make everything happen when it should. I tell you new information once a day, I can only tell tell you very little, but if I tell you new information once an hour hand, I can tell you 24 times as much. (clock is simple, faster is better, if your system can handle it)

Then there is the CAS (and RAS and T and a BUNCH of other things) which are rated in how many clocks (events) it takes to do steps with RAM. A CAS of 2, means it takes 2 events to do the CAS, a CAS of 2.5 means it takes 2 and 1/2, etc. (DDR means you can do things at the 1/2) You do CAS a lot, so having a smaller CAS, means you can do more stuff with the RAM, but that isn't the only thing that determines the speed of a system.

When the CAS makes the biggest difference, is when your CPU is using RAM the most. Again, that depends on the CPU, and the program/programs running. If most or all of you programs fit in cache, CAS can be silly high, and you'll see little difference, but if it can't, and you are using RAM all the time, it will make a HUGE difference.

Hope that helps.

If there is little difference in price, get the low CAS. If your system can use it, get faster (PC2100 is SLOW) RAM with the lower CAS that doesn't make a big price change.

[SHS]

As said by MattHelm Does CAS matter, it depends.
When come to 30-pin SIMM, 72-pin SIMM, 168-pin SDRAM and 184-pin DDR it rally dosen't matter you can mix match CL2 with CL3 it alway fall back to slowest Timings and Memory speed.
With 240-pin DDR2/3 this is a diff ball game you must match your latencies and Speed on and memory or you have problem.
You should noticed no diffrence between two cas timings as far as Performance gose but it usely a good idea to stick with same CAS latency.