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Mixing 2 sizes of OCZ on P5Q mobo

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macool

New Member
Joined
Sep 5, 2009
I have an Asus P5Q Premium motherboard and have 4GB (2x2) of OCZ DDR2 PC2-6400 Vista Performance Gold 4GB Dual Channel ram which works fine.

I have upgraded to Windows 7 Ultimate 64 bit and as I have another 2GB (2x1) of the same ram (OCZ Gold XTC OCZ2G8001G (2x1GB)) I thought I would be able to use it with the 64bit OS, but not so.

Both sets of ram work fine seperately but when I add the two 1GB sticks the PC starts (fans , lights, HDDs etc) but it won't boot or go into the BIOS. All settings in the BIOS are set to AUTO.

Although the ram is supposed to be the same speed, CPUZ reports the timings as different.

2x1 as 5 5 5 15
2x2 as 6 6 6 18

I have tried setting the timings manually in the BIOS to both sets of timings without success.

Although I have built a few machines in my time, I'm a newbie when it comes to ram timings.

Any suggestions would be welcome.

Thanks
 
You'll need to make sure you have 'em in the correct banks, both 1gbs in A or B and both 2gbs in the other.
The dual channel setup for two dimms puts one in A1 and one in B1, so if you add odd sizes to A2 and B2 you won't get real far.
Set all the timings to the slower timing, turn off dual channel, and look on the mobo for the A1/A2/B1/B2 markings.

Odds are performance will get worse though, you're cutting bandwidth in half by forcing single channel operation.
 
Hi Bobnova,
Yes I had them in dual channel setup and if they worked first off then fine, but as you suggested if there is going to be a performance drop then I suppose it's not worth the bother getting them to work together.

But it was worth the exercise to learn a bit more about ram.

Thanks for your help.
 
I think you forgot to clear cmos when you added both sets. you should set them both(all 4 sticks) to the 6-6-6-18 because that is the slower latency.

you will only get a major performance decrease if you don't have it in dual channel or can't set them at the rated speed. ddr2 800 /pc2 6400

what you should probably try is a compatible speed profile for both sets at a lower clock speed (mhz) then slowly go up and change the timings.

ie put in the slower sticks the ones rated 666 18, then set everything to manual, clock timing make it like ddr 667 (mhz)
(try 6-6-6-18 on the 2x1 set and see if they boot) if they do then you have 2 sets that will run at the same clock speed and same latency so the only problem is really how you don't know how to set them that way together.

turn off the computer, unplug, then add the 2 sticks of 555 15 and if you don't boot up then it's a bios setting that is not compatible.

you should make sure that your sets are in dual channel with each other and not with the mismatched sizes. (read the motherboard manual)

ideally if you can somehow load bios defaults with both sets (all 4 sticks) at slowest speed then you can go up from there.
 
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