Cas2 vs Cas3 ?

[oober goober]

Just what are the performance differences? Are they major? Anyone got any links or able to shed any light on the subject?
Thanks in advance
MiNIoN

[Nuno]

I´m no memory expert but I will tell here my personal experience. Maybe someone will care to comment about it.

For what I´ve seen, cas 2 makes *some* diference, not something you would really notice. I have an Athlon 600 + Gigabyte GA-7IX + 2 x 64 Dimms generic pc100. The motherboard bios has many options to tweak the memory, but I left it to auto. It assigned the folowing parameters to my ram:

SDRAM Trc Timing value 8
SDRAM Trp Timing value 3
SDRAM TRas Timing value 6
SDRAM CAS Latency 3
SDRAM Trcd Timing value 3

I could get than it was cas3, nothing else. Ok, the SDRAM dimms were cas3 for sure, cheap stuff. But I got in tweaking it. I changed CAS Latency to 2, rebooted, and it worked. It was stable, benchmarked it, and yes, there was a performance increase, but nothing worth talking about.

I got back into the bios settings and tweaked it by trial-and-error: didn´t really had a clue what I was doing, but in memory settings, lower is better, rigth?

So to sum it up I changed the settings above to:
4
2
2
2
2

And now, the sytem is stable, 3dmark99 went from 5750 to 5980 3dmarks, and the memory benchmark in sandra 2000 went to 370/434, higher than the reference Athlon 600 system.

So cas2 makes a difference? Yes. But tweaking other things does much more.

[Wombat]

CAS-2 memory is faster than CAS-3, but not by much. Maybe 2-3% noticable difference. However, if you plan on overclocking, CAS-2 memory has a better shot of making higher FSB speeds, even if you have to slow it down to CAS-3. I'm warning you, this is just a "maybe" type thing, nothing really tangible.

[oober goober]

Thanks for the input everyone - much appreciated. As it turns out I (think) I'll be getting Cas2 PC133 - that is if (as I suspect) Century is indeed Cas2.
I had Winbond Cas3 (for 2 weeks) but will move it on.
Cheers
MiNIoN

[Johnny Ray]

MiNIoN,

Wombat is right, as usual. You can actually see graphs of the performance between CAS2 and CAS3 at this site:

http://www.micron.com/mti/msp/html/speedoption.html

In fact, the Crucial site is a great (and accurate!) resource for answers to all your memory questions.

John

[Kruse]

I have two vanilla PC100 128 MB dimm modules (from what I gather, they're not CAS2 - mem speed is 8ns).

They run perfectly stable at 124 MHz CAS2. I also had a PC66 10ns module that worked fine at 124 MHz CAS3, but I haven't tried it at CAS2.

Switching from CAS3 to CAS2 and disabling Video Memory Caching/Shadowing cut down my SETI work unit time from 7 hours to 6. That's a VERY inpressive performance gain, but I haven't tried which of the options it comes from.

[Guacamole]

Wow, this discussion couldn't have come at a better time -- I'm was just considering between purchasing CAS2 and CAS3 RAM.

In terms of price, there isn't TOO much of a difference, but would PC100 CAS2, or PC133 CAS3 be better?

I have a PII-350 (to be upgraded to a P3-600e in about a month), Abit BX6r2, Win2K, G400DH oem. I do want to try some overclocking on this.

Thanks!

[mkaresh]

Excellent link, Johnny Ray. I just wish they specified what order they were using for 2-3-2. I think they use CAS, CAS to RAS, and Precharge RAS. If so, that's whay I'm using from 120 to 133. But the order in my BIOS (Award 4.51PG) is different:
RAS to CAS, Precharge RAS, CAS, so I until recently thought I was using 3-2-2.

So I wish Micron had made the order they were using clearer.

In case people don't know, the Futuremark test is probably 3dmark99.

[Wombat]

Guacamole:
I'd go for the PC133. Otherwise you'll really wish you had it later. Also, odds are good that it will do CAS2 @ 100MHz.

[RAB]

Go here: http://www.overclockin.com/reviews/R...oundup2-2.html

RAB


[This message has been edited by RAB (edited 10 March 2000).]