Mixing two sticks of DUAL Channel with two identical sticks from a QUAD channel set

[Dave FromKent]

Hi, I've checked the previous questions, but none quite fit with my query.

I've got a 16gb dual set of G Skill 8GB Tridentx Cas 10, 2400 DDR3. I use the Z87 ASRock Xtreme 9ac which has four slots and a max of 32gb.

I've got the chance to buy a pair of G Skill 8GB Tridentx Cas 10, 2400 DDR3. They match the specs of my existing set exactly, but they are from a QUAD set (dunno why only has two but he hasn't so I can't get the quad set!!)

So, the four sticks match. Same cas, same speed, same brand, same mark, same voltage, same color, same everything. They are identical except that two are a dual set and the other two are a pair from a quad set.

I have asked G Skill who helpfully emailed me and told me that they can't guarantee compatibility, but might work if I lower the speed and fiddle with the voltage. I get what they are saying, but I don't need a guarantee! I need them to work!

Question is, will they work, or won't they? Do I need to fiddle with the voltages? I don't really feel confident enough to muck around with the RAM settings.

I'm looking at getting them cheap, but not so cheap that I can afford to get something that doesn't work. I doubt it is easy to sell half of a quad set on fleabay!

Thanks very much all.

 

[digitaldoc]

The simple answer is, unless the set of RAM is bought as a single kit, there is no guarantee that they will work. This is true, even if the sticks all have the same exact specs.

 

[Dave FromKent]

I get that, but why?!

 

[digitaldoc]

When RAM is manufactured, it needs to be from a matched set so it will have compatibility with the other sticks. When you mix RAM from different runs, and from different manufacturers, it may not play nicely together.

 

[rgd1101]

I get that, but why?!

because it a high tech sensitive electronic.

 

[joex444]

I have asked G Skill who helpfully emailed me and told me that they can't guarantee compatibility, but might work if I lower the speed and fiddle with the voltage. I get what they are saying, but I don't need a guarantee! I need them to work!

Question is, will they work, or won't they?

Quite honestly, there's nothing about your situation that's different than the common question of "I have one stick of memory, can I add another?". The only apparent difference is you have a matched pair and are trying to add another matched pair. While 1 and 2 would play nicely together, and 3 and 4 would play nicely together you also need to ensure 1 and 3, 2 and 3, 1 and 4, and 2 and 4 all play nicely together as well. So you see there is but one match that needs to be made in the case of 2 sticks, but 6 in the case of 4 sticks. Of those 6 combinations, we only know for sure that 2 of them are OK. Any, or all, of those other 4 may not be OK.

The short and long of it is matched sets are guaranteed to work, unmatched sets do not have a guarantee. This is why you're not getting a "straight answer" from anyone -- there's no guarantee. We -- neither G.Skill, I, or any one else -- can guarantee you that these would work just fine. We also cannot guarantee you that they wouldn't. Typically, in the case of 1 stick added to another stick there's about a 97% chance it works *if* it's from the same company with the same specs. Based on this, and the fact that's *one* combination but you need *four* to work the odds that it would work is the probability of the one combination (97%) to the fourth power (if P=0.97, then this is P^4), or about 88%. Figure there's an 85-90% chance it would work.

 

[Dave FromKent]

Cheers Joe, those are good odds. I'm buying. And as I said, I'm not looking for guarantees, just a reason why they might not work.

 

[Tradesman1]

I cover this in my article here:

http://www.tomshardware.com/reviews/ddr-dram-myths,4155.html

in particular items 6 and 2, it basically comes down to it's a 50/50 crapshoot if they will play, and with this particular like (the 2400 sticks, maybe a little less as they've changed the mory chips used - the initial sets had Hynix chips which were later changed to Samsung chips - if you try and have problems give me a shout, the Tri's are my favorites for Haswell and have used and tested/played with a bunch of the sets - have 'em in both my Haswell rigs (in sig)

 

[biggies]

I have asked G Skill who helpfully emailed me and told me that they can't guarantee compatibility, but might work if I lower the speed and fiddle with the voltage. I get what they are saying, but I don't need a guarantee! I need them to work!

Question is, will they work, or won't they?

Quite honestly, there's nothing about your situation that's different than the common question of "I have one stick of memory, can I add another?". The only apparent difference is you have a matched pair and are trying to add another matched pair. While 1 and 2 would play nicely together, and 3 and 4 would play nicely together you also need to ensure 1 and 3, 2 and 3, 1 and 4, and 2 and 4 all play nicely together as well. So you see there is but one match that needs to be made in the case of 2 sticks, but 6 in the case of 4 sticks. Of those 6 combinations, we only know for sure that 2 of them are OK. Any, or all, of those other 4 may not be OK.

The short and long of it is matched sets are guaranteed to work, unmatched sets do not have a guarantee. This is why you're not getting a "straight answer" from anyone -- there's no guarantee. We -- neither G.Skill, I, or any one else -- can guarantee you that these would work just fine. We also cannot guarantee you that they wouldn't. Typically, in the case of 1 stick added to another stick there's about a 97% chance it works *if* it's from the same company with the same specs. Based on this, and the fact that's *one* combination but you need *four* to work the odds that it would work is the probability of the one combination (97%) to the fourth power (if P=0.97, then this is P^4), or about 88%. Figure there's an 85-90% chance it would work.

Where did you get 97%?