DDR2 Memory problem

Jakmeehan

Hello all,

I currently have a Dell XPS 720 with 5GB of DDR2 PC6400 RAM installed.
The configuration I have is;
3 x 1GB PC6400
1 x 2GB PC6400

The problem is that when all 5GB is installed, the bios is only reading the Memory speed as 667mhz, whereas when I have either the 2gb module installed on its own, or any of the 1gb modules installed without the 2gb module then the speed is 800mhz.

Does anyone know why this is?
Would installing 2 x 2gb PC6400 modules and 2 x 1gb PC6400 modules fix this problem, do you think?

Thanks in advance for all help!

lmimmfn

memory works on the lowest common denominator, i.e. the lowest spec memory will drag the rest down, especially in a Dell where you cant manually configure the mem( unless they've changed )

Are you sure the 2Gig stick is 6400 ram? if so it could be that the other mem has tighter timings( i.e. latency such as 5-5-5-18 ) than the 2gig stick, so rather than match the speed with the 2 gig stick it reduces the speed of all ram because of the timings.

Can you force the latencies in the bios?

Jakmeehan

lmimmfn wrote: »

memory works on the lowest common denominator, i.e. the lowest spec memory will drag the rest down, especially in a Dell where you cant manually configure the mem( unless they've changed )

Are you sure the 2Gig stick is 6400 ram? if so it could be that the other mem has tighter timings( i.e. latency such as 5-5-5-18 ) than the 2gig stick, so rather than match the speed with the 2 gig stick it reduces the speed of all ram because of the timings.

Can you force the latencies in the bios?

Thanks for your reply.

The 1gb modules are pc6400u-555-12 and the 2gb module is pc6400u-666.

I'm not sure if that refers to the latencies or what though.

What do you think?
I don't think I can force latencies either, but I could be wrong. How would I check?

lmimmfn

Jakmeehan wrote: »

Thanks for your reply.

The 1gb modules are pc6400u-555-12 and the 2gb module is pc6400u-666.

I'm not sure if that refers to the latencies or what though.

What do you think?
I don't think I can force latencies either, but I could be wrong. How would I check?

yes the 555-12 refers to the latencies for CAS/TRCD/TRP and TRAS.

Check in the bios if you can change the latencies for timings for the ram, i seriously doubt it as Dell butcher their Bios's to prevent you doing anything really.

At the end of the day if you benchmarked i would seriously doubt there would be any performance difference from you running the ram at 667 rather than 800

Jakmeehan

lmimmfn wrote: »

yes the 555-12 refers to the latencies for CAS/TRCD/TRP and TRAS.

Check in the bios if you can change the latencies for timings for the ram, i seriously doubt it as Dell butcher their Bios's to prevent you doing anything really.

At the end of the day if you benchmarked i would seriously doubt there would be any performance difference from you running the ram at 667 rather than 800

You're right, I can't change a thing in the bios. I now have 7gb total (3x2gb, 1x1gb) which i'll continue to run at 667mhz instead of running 4gb at 800mhz.

Thanks very much for your help