Memory speed

[hilikus]

Hello,
i have 3 sets of DIMMS, 1 is a kit of 2x1GB stick (lets call it A), the other is 1x1GB stick (B) and the last one is a stick i bought yesterday, 1x2GB (C). All sticks are rated for 800MHz and when i put each set separately the BIOS detects them at 800MHz. When i put A & B (so 3 sticks total), it still detects them at 800MHz, but when i put A & C (3 sticks total) or B & C (3 sticks total) or A & B & C (4 sticks total) it detects them at 667MHz.

So I have two questions
1) What could be causing the memory controller to underclock the memory even when each set separately is correctly clocked at 800MHz
2) is it worth it to manually set the speed to 800MHz? i don't know if this would be considered overclocking since the sticks are rated at 800MHz after all. And by worth it i mean, will it have a real impact on my everyday usage? (the only heavy stuff i do is compiling code and runnings VMs)

BTW, all this is in single-channel mode. I gave up with the dual channel mode a long time ago

 

[ahnilated]

A lot of older motherboards would down clock when you put 4 chips in because the memory wouldn't run at full speeds across all 4 slots.

 

[willard]

BTW, all this is in single-channel mode. I gave up with the dual channel mode a long time ago

Unsurprising, mixing and matching causes lots of issues with dual channel mode, and you mixed and matched about as much as could possibly be done. At the very least they need to be the same capacities, which in your case they are not.

As far as why they are detected at weird speeds when mixed and matched, it's probably related to the same issue. Your motherboard is getting confused by the degree to which you've mixed your memory types. Just go and set the speeds manually.

 

[hilikus]

They are not as mixed as it sounds

2 of the 4 are a kit and these 2 are in its own module obviously. All 4 are of the same speed (PC2-6400/800MHz). Really the only curve ball is the capacity of the new stick

I was hoping that the whole dual-channel mode could be isolated at a per-module level. So module 1 with its two identical sticks could work in dual channel mode, while the second module with sticks of different capacity would run in single channel mode. But i guess i was wrong. Which is ok, i keep finding info about how dual-channel mode is only a theoretical gain not having a big impact in common usage. What i did not expect was that even though the sticks by themselves are detected at the right clock speed, would not be detected correctly when mixed. In the worst case just with 2 sticks (the new and one of the old ones) makes it already be underclocked

 

[willard]

They are not as mixed as it sounds

Yes they are. You have a dual channel kit plus two single modules. That's already VERY mixed. Throw in the fact that you've got modules at both 1GB and 2GB and the situation only gets worse.

That is very, very mixed up.

I was hoping that the whole dual-channel mode could be isolated at a per-module level. So module 1 with its two identical sticks could work in dual channel mode, while the second module with sticks of different capacity would run in single channel mode.

Nope, your motherboard either operates in multi channel mode or not. You'd get weird and totally unpredictable performance penalties based on which modules were being read from, and it would be different each time. This is also why all modules must run at the same speed.

Which is ok, i keep finding info about how dual-channel mode is only a theoretical gain not having a big impact in common usage.

That is correct. Memory speed has remarkably little impact on your computer's performance outside very specific cases. For example, the difference between DDR3-1600 and DDR3-2800 is almost nil for gaming, despite the massive difference in speed.

 

[hilikus]

Thanks for the answer willard

So IIUC you are saying that the reason they are underclocked is just because the mobo is confused due to the mixing and not because there might be some stability reason or something more significant? i'm just wondering if i should manually override the memory clock speed or leave the automatic one. I don't know how good these automatic detections are

 

[willard]

Just set the clocks back to 800 MHz. If it's unstable, undo it. Simple as that.

 

[hilikus]

Got it, thanks a lot!

 

[hilikus]

Best answer selected by hilikus.

 

[nikorr]

This topic has been closed by Nikorr