PC 133, CAS 2 versus CAS 3

[bunn47]

I'm confused about the performance difference I would expect from PC 133 CAS 2 versus PC 133 CAS 3 memory? What kind of difference would one expect in game performance?

Also, I just purchased a 128 MB stick of Infinion PC 133 CAS (maybe 2 maybe 3). I ordered CAS2, the lable on the stick says CL3. When I emailed the tech people where I bought the memory, they replied that a)They test each memory stick and it is CAS 2; b)They spoke to the manufacturer and were told the lable was a boo boo (my term). Does this sound right? I'm new at this so I have no experience for what is correct but I'm getting a funny feeling that something aint quite right here. Please help.

[Dputiger]

You always want to run at CAS2. CAS stands for Column Access Strobe. Basically, this is a measurement of latency--CAS2 is also called CL2.

So, your CAS-2 RAM will have a 2 ms latency, while your CAS-3 RAM has a 3 ms latency. If you use a program like Sandra, set for both and compare the memory benchmark--you'll notice a fairly dramatic difference.

Also, if you can, raise your DIMM timing as high as it can go. This will help increase memory speed as well.


As to whether or not your memory can handle it, just set a setting and reboot. If the computer boots and runs without a problem, try it again. http://sysopt.earthweb.com/forum/smile.gif

[Roy]

bunn47 ~ Maybe you're being given a run-around. Are you talking about a paper label on the stick itself? To be sure, go to the chip maker's web site and find out what the specs are for the part number on the chips. Infineon is a product of Siemens.

And, Dputiger, that's not quite correct.

CAS Latency is the number of clock cycles between a request for data and the availability of that data. With a 100MHz FSB, there are 100,000 clock cycles each milisecond.

CAS Latency is an indication of SDRAM's maximum speed capability. PC100/CL2 might run as fast as 133MHz, but at speeds upwards of about 120, a CL=3 setting usually is required for stable running.

Another gauge of speed is Clock Cycle Time (tCK). 133MHz=7.5ns. PC133 RAM with tCK=7ns is good up to 155MHz.

Don't be taken in by vendors who try to sell SDRAM by saying it's "6ns". They're talking about Clock Access Time (tAC). Make sure to know which one is expressed.

In real life use, the difference in performance between the two settings is difficult to notice. That is, assuming you're able to run at the lower number CL setting.

[Whir]

How do you up DIMM timing? Is that in the BIOS? Just curious.

[Dputiger]

Whir: Yes, if you can change it. Some BIOSes dont' allow for DIMM timing changes.


Roy: How is that different than what I said? I'm not trying to be snotty--I don't quite see the difference. http://sysopt.earthweb.com/forum/smile.gif

[Nathan G]

Nice Reply there Roy!
Thing is, Sandra has reported considerable improvements in benchmarks by decreasing cas setting in BIOS.
BTW.. My accountant gets REALLY pissed when I start slinging around the decimal points like that. err +/- 6 places.



[This message has been edited by Nathan G (edited 07-21-2000).]

[Roy]

Dputiger ~ It's the part about the milliseconds. We're talking nanoseconds here, big difference! http://sysopt.earthweb.com/forum/wink.gif

You'll also note I'm picky about it being the CAS latency. A so-so analogy would be the difference between going 65 miles, and 65 miles per hour.