800 Mhz RAM only running at 666 MHz

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kcheleb

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Jun 22, 2012
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Hello, my cousin at his workshop has a fairly old custom built computer with the following motherboard:

XFX Nvidia NFORCE 680i LT SLI (Socket 775) motherboard

he only had 2 GB DDR2 RAM (running at 800 Mhz) on the computer and wanted to upgrade, so I advised him to get the Crucial 2 GB DDR2 CT25664AA800 RAM ..

the RAM he originally had was Corsair CM2X1024-6400C5DHX


so I installed the new Crucial RAM for him and ran Speccy, it shows that yes he now has 4 GB ram however the DRAM is at 333.3 MHZ, or in other words 666 Mhz frequency

why is it running at 666 Mhz frequency when both RAMS are 800 MHz

thank you
 
Solution
D
Although written as 1333 the actual FSB is 333. The reason behind this is that the FSB on a Core2Quad is 'quad' pumped or does 4 information transfers per cycle. For our purposes we only need to be concerned with the true FSB which is 333. 4 x 333 = 1333.

The RAM is DDR or double data rate. Meaning although it is listed at 667 this is the effective speed and the actual speed is 333Mhz. DDR ram is 'double pumped' since information is sent on the falling and raising edges of the clock cycle. All DDR is like this and will read the correct speed in CPU-Z. So DDR3 1600 really runs at 800Mhz and CPU-Z reads it as such.

So when we read the actual FSB of the processor ( 333Mhz ) and the actual speed of the RAM ( 333Mhz ) we get a 1:1 ratio...
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Go into the BIOS and check your ram speeds.
 
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You might need to pop into the BIOS and instead of using the by SPD option, fiddle with some speed & timing options until it can be dialed in. Do they both report 800MHz individually?

Make sure you know where to reset his BIOS as you may get into an un-bootable state doing this.
 
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I actually did try doing that but I don't even know where to go, he has an old Phoenix BIOS , I don't think there was even an option to overclock the RAM there, either way I don't feel comfortable overclocking the old DDR2 ram, I thought you were only capable of doing that with the newer DDR3 ones with the XMP set profile
 
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There should be presets for the ram frequency you don't have to overclock. Just look around for anything like that.
 
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With a Core2 it does not matter. Core2 runs best with the FSB and RAM at a 1:1 ratio. Meaning DDR2 800 and 1066 was mostly useful on overclocked CPUs. What CPU does he have?
 
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Unchecking SPD(Serial Presence Detect) isn't overclocking. It just means the default settings of the RAM on its ROM chip, aren't compatible with what you're trying to do and you would like to manually configure timings and speed. A BIOS could limit how much you are able to do or see though....
 
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Although written as 1333 the actual FSB is 333. The reason behind this is that the FSB on a Core2Quad is 'quad' pumped or does 4 information transfers per cycle. For our purposes we only need to be concerned with the true FSB which is 333. 4 x 333 = 1333.

The RAM is DDR or double data rate. Meaning although it is listed at 667 this is the effective speed and the actual speed is 333Mhz. DDR ram is 'double pumped' since information is sent on the falling and raising edges of the clock cycle. All DDR is like this and will read the correct speed in CPU-Z. So DDR3 1600 really runs at 800Mhz and CPU-Z reads it as such.

So when we read the actual FSB of the processor ( 333Mhz ) and the actual speed of the RAM ( 333Mhz ) we get a 1:1 ratio :)

That Chip uses a relatively low 7.5 multiplier to reach it's stock speed. The core clock of a Core2 CPU is the chips multiplier x FSB. so you take the FSB of 333 x 7.5 = 2.5Ghz.

This is easier to understand if we take a chip like the E8400 with a nice easy 9x multiplier. The multi of 9 x 333FSB = clockspeed of 3Ghz.

Now if overclocking, to maintain the 1:1 RAM.FSB ratio we need DDR2 800 because to overclock the E8400 we have to raise the FSB ( multipliers are locked ) So to reach an easy 3.6Ghz we raise the FSB to 400 thus needing DDR2 800 ( also running at a true 400 since it's DDR ) to keep the FSB/RAM ratio. 9x multi x 400Mhz FSB = 3.6Ghz

Does that help or just confuse you more? lol

Either way I know what I'm talking about and DDR2 667 is fine with that CPU. LGA 775 was around for years and I overclocked more of them than any other socket type.
 
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Solution
Yeah it's fine. 😉

You could also enable XMP or manually set the RAM speed in BIOS to run at its rated speed. All I was getting at is that it does not matter and there will be almost 0 performance gain.
 
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But since adding the extra 2 GB of ram I haven't really noticed an improvement on the performance of the desktop, it doesn't open programs or anything any faster now
 
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No adding RAM is not going to make anything run faster except in cases of multitasking were you were running out of RAM before. I suspect with only 2GB you could browse the internet reasonably well as long as you kept it to a few tabs open at the same time. And that was about it. 4GB will help significantly with multitasking.
 
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