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Ram speeds

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February 12, 2010 5:44:51 AM

I'm fairly new at overclocking, so sorry if I ask something trivial :-)

Gear: i7-860, Asus P7P55D-E Pro board, 4Gigs of 1600MHz RAM

I think I managed to get a stable OC at 160 BCLK, but I have a question concerning the RAM.
My RAM is rated at 1600MHz, with 8-8-8-24 timings at 1.65V,
So this is what I filled in in the BIOS. The 160BCLK allowed me to pick a ratio that brings my RAM speed right at 1600MHz.

The thing is though, that my motherboard's software (at runtime in OS) can make my BCLK go in "Turbo" mode (+5MHz). This of course lifts my RAM speeds up to +/- 1650MHz.
Is this dangerous? I read some forums where people said, never to go over your rated RAM speeds. So should I really downclock my BCLK speed to 155MHz, just to make sure that the "Turbo" doesn't drive my RAM speed above 1600MHz?

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February 12, 2010 8:46:36 AM

Dangerous in what sense? Your PC wouldn't explode. but it may cause memory errors. I assume you ran memtest86+ numerous times? Without this utility, you should not attempt any overclocking at all.

I'm also assumng you know how to stress test your CPU, to verify the system is running rock stable with the selected settings. Also, you do know memory performance is a non-issue these days?
February 12, 2010 9:07:25 AM

Thanks for your reply.

I did indeed verify my system is stable, by running some long Prime95 tests.

I have memtest86+ and ran it, but I'm not sure when to use it. I mean, it's a non-windows program, so it would only be able to test my RAM at the rated speed (1600MHz). Which would still not prove if I can run it without errors if its gets to 1650MHz in windows (because of the "turbo" mode). Correct me if I'm wrong please.

I do not know what you mean with memory performance being a non-issue. I am by no means trying to overclock my RAM, I just wonder if the added MHz on the rated speed, is "a lot more" or "only a slight increase", when it comes to RAM stability.
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February 12, 2010 9:23:33 AM
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DDR3-1600 runs at 400MHz actually, but as its quad-pumped it would mean it provides as much bandwidth as 1600MHz DDR1 - but not the same latencies!

My point on memory performance being a non-issue is that memory performance is very high already, and doesn't affect performance of common home tasks to any significant degree. The difference in real applications between the slowest RAM and fastest RAM is only modest (5-10% at best). Only in synthetic benchmarks or very specific applications will you see larger performance increases.

If you overclock from 1600MHz to 1650MHz that's a slight overclock yes - but it may cause memory timing problems. It IS overclocking, just a rather convenient/easy way to do it.

Normally these are BIOS-controlled though. If you use in-Windows overclocking, you can indeed not use Memtest86+ to confirm it runs rock stable at those settings. You may try Prime95 and use the Torture test/Blend benchmark to test if your memory is stable, but it won't be able to test the memory regions that are reserved by Windows. There's a slight chance your memory may produce errors undetectable with an in-windows memory test.

If possible, do all the overclocking in BIOS instead, so you can indeed use Memtest86+ to confirm its running stable. Let it make 1 or 2 passes, at least.
February 12, 2010 10:11:26 AM

In understand (but I thought DDR3 was just double-pumped, meaning it ran at 800MHz)

I don't see how the timings might slow down, since they are specifically inputted in the BIOS. So I guess the only thing that can change while in windows is the BCLK speed and thus because of the set CPU-Memory ratio, my RAM speed? Or doesn't it always follow the BIOS settings?

Basically I could overclock my BCLK in BIOS so that the ram runs at 1650MHz, and then run Memtest86+. If it proves to be stable, I can reset the BCLK to my initial settings without worrying when in windows it increases with 5MHz again. Right?

By the way, would you then recommend trying to run my memory slower, but with tighter timings?
February 12, 2010 4:54:17 PM

DDR1 400MHz = 400MHz x 1 = 400MHz effectively
DDR2 400MHz = 400MHz x 2 = 800MHz effectively (double data rate)
DDR3 400MHz = 400MHz x 4 = 1600MHz effectively (double double data rate; quad-pumped)

The down-side is, the CAS/RAS timings increase with each step. DDR3 has much higher latencies than the CL2.0 timings possible with DDR1. So, DDR3 needs to have alot more bandwidth/throughput to compensate for those higher timings.

The timings are stored in the JEDEC-spec compatible "SPD" of the memory module. This serves as 'advice' to the motherboard BIOS, which can follow these 'guaranteed' settings/timings or set its own timings/clock rates; either lower than the spec or higher. So the BIOS controls the speed. If the memory can't keep up, it will produce errors or not even let the computer boot. Then you need to perform a CMOS reset (jumper on your motherboard) to reset these settings.

However, after booting windows, you can use software like the one you already used, to change the clock settings afterwards, while the system is running. Your idea of BIOS-overclocking to allow you to test with Memtest86+ and then changing it to use software-overclocking in Windows instead, is a good idea. :) 

If you want, you can experiment with changing timings etc. Be sure to know how to clear CMOS data before you attempt this, though!
February 12, 2010 11:40:15 PM

Ok, thank you very much. This helps me a lot!
February 12, 2010 11:40:56 PM

Best answer selected by Falx.
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