Do two DIMMs have to be identical if there in the same channel?

[irsninja]

?

 

[bucknutty]

No, you can mix and match any way you want. I have seen systems with 1600ddr3 and 1333 ddr3 and they run at 1333 ddr3 dual channel, and run great.
I have a core 2 duo with 2 sticks of ddr2 1 at 667 and 1 at 800 and 2x 512 sticks at 667. This system runs dual channel at 667 and has been going strong as a htpc for like 4 years now.

Just run the mem test cd or memorytest from windows 7 to make sure it works.

An exact match will guarantee proper functionality, so it is the recommended way to go.

 

[wiinippongamer]

It's not absolutely necessary though recommended, but they do have to be set to run at the same voltage, frequency and timings AND preferably the same size, as long as they meet those requirements they should work as intended regardless of brand.

I the sticks have different specs they'll adjust automatically to match the slowest stick.

 

[arson94]

If you mean to run them in dual-channel mode then it is highly recommended to have identical DIMMs for stability and best overall performance. As far as I know, it's not required, but the ability to run two DIMMs with different specifications in dual-channel mode just depends on how well the memory controller can manage it and will differ from controller to controller.

EDIT: buckutty and wiinippongamer replied as I was typing. We all agree though I think.

 

[willard]

In general, no, but in rare cases you can get weird issues. It's best to run true dual channel kits whenever possible. With DDR3 being so cheap right now, there's really no reason not to outside really old systems (DDR2 is so expensive I'd sooner replace the motherboard than buy more memory).

 

[bucknutty]

Good point wiinippon, to run dual channel both sticks in the channel must be the same size. So in channel 1 you can have 2x 1gb and in channel 2 you can have 2x512. But if all you have is 1 1gb and 1 512 you can not run dual channel, but the system will still run correctly, only a tiny bit slower.

 

[Branden]

most mobos will work fine if DIMMs aren't the same (but you likely won't get optimal performance from them), and some (cheaper) mobos won't even post with dis-similar sticks.
best to use identical sticks and avoid potential issues.

 

[wiinippongamer]

I have a core 2 duo with 2 sticks of ddr2 1 at 667 and 1 at 800 and 2x 512 sticks at 667. This system runs dual channel at 667 and has been going strong as a htpc for like 4 years now.

So it has 5 sticks?, that ain't dual channel.


Edit - wow this thread filled up pretty quick.


I've seen reports of people running different stick sizes on dual channel with a cpu-z screen to back it up, but it's highly unlikely one can manage to get them running like that and it'll require some extra tweaking and luck with the parts, so yea better leave it at that they need to be the same size.

 

[irsninja]

so from what I understand, they dont have to be the same, but should be same voltage and size to be in the same channel, but its ok to have 2x512 and 2x2gb in different channels?

 

[bucknutty]

So it has 5 sticks?, that ain't dual channel.

no it has 4 sticks of ddr2.
1x 1gbt ddr2 667
1x 1gbt ddr2 800
1x 512mb at ddr2 667
1x 512mb at ddr2 667

total of 3gb running at dual channel 667mhz.

 

[bucknutty]

so from what I understand, they dont have to be the same, but should be same voltage and size to be in the same channel, but its ok to have 2x512 and 2x2gb in different channels?

correct. And many times a quality board will read the memory spd and as long as the 2 dimms have a set of matching voltages, timings, and speeds it will choose the match and enable dual channel.

 

[InvalidError]

so from what I understand, they dont have to be the same, but should be same voltage and size to be in the same channel, but its ok to have 2x512 and 2x2gb in different channels?

For best results performance-wise, slot 1 in channel 1 should be the same type (edit: read as in same physical DRAM and DIMM chip organization) as slot 1 in channel 2, likewise for slot 2 to make the memory configuration symmetrical and enable the memory controller to run the memory as a single 128 bits bus.

 

[irsninja]

For best results performance-wise, slot 1 in channel 1 should be the same type (edit: read as in same physical DRAM and DIMM chip organization) as slot 1 in channel 2, likewise for slot 2 to make the memory configuration symmetrical and enable the memory controller to run the memory as a single 128 bits bus.

so it should be like this?

slot 1 channel 1 2gb
slot 2 channel 1 512mb
slot 1 channel 2 2gb
slot 2 channel 2 512mb

with the 2gb and 512mb being identical

 

[InvalidError]

so it should be like this?

Ideally, yes.

Some motherboard/BIOS/CPU/DIMM combinations may be touchy about arrangements but this one is technically the best when it works, which it should.

 

[bucknutty]

so it should be like this?

slot 1 channel 1 2gb
slot 2 channel 1 512mb
slot 1 channel 2 2gb
slot 2 channel 2 512mb

with the 2gb and 512mb being identical

Often times the slots are color coded. So you want the 2x 2gbs in the black, slot o and slot 2. Those should be the 1st channel.
Then put the 2x 512s in the blue slot 1 and slot 3. That should be channel 2.
slot 1 channel 1 2gb
slot 2 channel 2 512mb
slot 3 channel 1 2gb
slot 4 channel 2 512mb

If it were me i would probablly skip the 512s... I mean most programs will run very well at 4 gigs, and the 1 extra gig may offer very little in the way of a performance lift. And if the 512s are slower they will cause all 4 sticks to clock down to match them. So adding the 2x512 may make the total system slower.

 

[InvalidError]

And if the 512s are slower they will cause all 4 sticks to clock down to match them. So adding the 2x512 may make the total system slower.

OP hasn't said what type of DIMMs he had. If they're DDR3 and the slower DIMMs are 1333 then there is no point about worrying about down-clocking. The 5th GB of RAM would most likely have a much greater performance benefit than the ~1% going from 1333 to 1600. For DDR2, 666 vs 800 might be a closer call depending on how OP uses his PC.

 

[bucknutty]

OP hasn't said what type of DIMMs he had. If they're DDR3 and the slower DIMMs are 1333 then there is no point about worrying about down-clocking. The 5th GB of RAM would most likely have a much greater performance benefit than the ~1% going from 1333 to 1600. For DDR2, 666 vs 800 might be a closer call depending on how OP uses his PC.

Very good point for the OP to think on.

 

[bucknutty]

If your lucky your board is color coded and you just put the matching sticks in the same color.