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Memory Speed and CAS latency awesomeness!

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  • Memory
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February 15, 2007 7:20:07 PM

Lets say that i get some good ol' ddr2-800 G.Skill CAS 5 RAM.
Can i underclock it to 533mhz (on a core 2 duo), and lower the CAS to 2?
Wouldn't that offer a performance increase as long as I don't overclock?
533mhz vs. 800mhz on a stock setup is an equal contest right?

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February 15, 2007 8:05:48 PM

First, i doubt you'll be able to get it down to 2. You could probably hit 3, maybe 2.5, but I doubt 2. Sorry, I'm to lazy to do the math right now as to which is faster. (533@CL3, or 800@CL5) This also assumes a 1:1 memory ratio, you can change the ratio to allow the 800 ram to run at its default settings. Whether or not this helps depends on whether the task is memory bandwith starved or not.
February 15, 2007 8:13:08 PM

Quote:
Lets say that i get some good ol' ddr2-800 G.Skill CAS 5 RAM.
Can i underclock it to 533mhz (on a core 2 duo), and lower the CAS to 2?
Wouldn't that offer a performance increase as long as I don't overclock?
533mhz vs. 800mhz on a stock setup is an equal contest right?


"[O]n a core 2 duo" is irrelevant, you want to be looking at the motherboard, or more specifically, its chipset. To answer your question about "533 vs 800", the answer is simply no.

When you start up your computer activate the BIOS by hitting F1, F2, F11 the delete key, or whatever the screen says to activate the BIOS. If you're not familair with it, it'll look really blocky with everything.

For my own motherboard I had to go into Chipset something to muck with the memory. For myself I could set the speed of my memory to 400, 533, or 667 speed, and 3, 4, or 5 for CAS latency. I'm assuming that CAS 3 is the lowest supported speed for DDR2 RAM, but I could be mistaken.

Past tests that I've read about say that for every full stepping of RAM speed (400 -> 533 -> 667 ->800) with a corresponding increase of CAS latency (3 -> 4 -> 5-> 6) shows an improvement of approximately 4% overall.

Underclocking, unless for cooling purposes, will be almost pointless. My opinion anyway.

Disclaimer: I know almost nothing about this kind of stuff. Someone more knowledgeable then me should post and either back-up or refute the above. For the original poster's safety.

Edit: I type too slow, follow the advice above.
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February 16, 2007 3:25:11 AM

If I were you, I would download SiSoftware Sandra and do some tests. Under benchmarks, choose the one that says memory bandwidth. Try different memory speeds and timing ratios until you get the most out of it. Always follow up sandra with orthos or something similar to test for stability and/or vice versa. Try to find the sweet spot where you get the most stability at optimal memory speed or should I say memory peformance.

Cappster
February 16, 2007 6:03:42 AM

The gist of your question seems to be "can I buy 800cas5 and clock to 533 to lower the cas?" In that case, yes, likely you can.
February 16, 2007 3:53:21 PM

Yeah, basically that's it.
I'm sorry if I missed it, but IF i did buy 800mhz ddr2, at CAS5, would it be more beneficial to underclock it to 533mhz, which still saturates the bus, and lower the CAS to 3 or w/e, so it is faster in that respect. Or, would it be better to keep it at 800mhz CAS5?

Sorry if i missed the answer to this question in the replies:::
February 16, 2007 4:37:12 PM

DDR2 don't usually down low to 2cas and lowering from 800 to 533 will slow it down regardless of the tighter timing. Try adding more voltage and tighten the timings at 800 or increase frequency at the same timing.
February 16, 2007 5:00:56 PM

I see, thanks for the help in my theoretical question.
February 16, 2007 5:06:10 PM

From what little I know, 800 Mhz CL5 always beats 533 CL3 (unless the timings get silly) To get more general-purpose speed, use the highest CPU multiplier and 1:1 ratio. Then set the timings a low as possible.
February 16, 2007 5:07:54 PM

From what little I know, 800 Mhz CL5 always beats 533 CL3 (unless the timings get silly) To get more general-purpose speed, use the highest CPU multiplier and 1:1 ratio. Then set the timings a low as possible.
February 16, 2007 7:46:25 PM

Yeah, but with gaming, I doubt It'll be better, so thanks guys.
February 16, 2007 8:00:47 PM

Quote:
From what little I know, 800 Mhz CL5 always beats 533 CL3 (unless the timings get silly) To get more general-purpose speed, use the highest CPU multiplier and 1:1 ratio. Then set the timings a low as possible.

Depends on what type of applications you will be running, for synthetic benchmarking and latency related applications, I think the cl3 would perform better

You're right. That is why I said "general-purpose speed". :D 
February 17, 2007 1:09:52 AM

yeah, thought so.
February 17, 2007 2:25:11 PM

Me?
This is all theoretical, WHEN i build my compy I'll probably have a 8800GTS 320 meg or a 8600GT/U.
In my sh1tty Pentium 3 i have an fx5500, which i added for a whopping 30 bucks so I could play quake3.
!