Is it risky to purchase two kits of 64GB RAM instead of single kit of 128GB RAM?

Question

Manufacturers of RAM, specially gaming RAM, sell 64GB kits of RAM (4 x 16GB modules), and also 128GB Kits (8 x 16GB modules). In one of the reviews of 64GB G.Skills Ripjaws V kit, one customer says that:

G.Skill and most memory makers do not guarantee two kits of RAM to work together. So if you are hoping to use two of these kits on a MB that supports 8 x 16GB RAM, you would be better off buying a single 8 x 16GB kit instead.

What is the meaning of not giving a guarantee that two 64GB kits will work together? I am asking since two 64GB kits like the ones mentioned would cost $510, whereas a single kit like this would cost much more, more than $600.

My question is, is it risky, might not work most of the time or sometimes, or causes problems only when overclocked? If anyone with experience can answer it would be helpful. I am assuming the motherboard can CPU can take 128GB RAM.

My own experience and search says the setup of two kits should work, since I have seen modules purchased at different times work together (one original, and second as update later, same manufacturer but different series). If speeds are different, system adjusts to the lower speed. If the configuration is not optimal, like 2 modules in slot 1A and 2A instead of slot 1A and 1B in dual channel gives warning on boot but otherwise works fine. Also kits are matched to give best performance but separately purchased modules of RAM should work fine, maybe a little slower, according to my understanding.

So is it a high risk purchase, low risk purchase or best avoided and my understanding is incorrect?

Answer 1

What is a matched set?

Matched sets are guaranteed to work together at advertised speed, assuming no motherboard incompatibilities or defects. 2 sets of same speed, same brand and same model number are not guaranteed to work well together. It's better if they come from the same production batch, but that still does not equate a matched set, as from what I understand a matched set has been tested (to a degree) during the binning process.

Number of sticks

In addition to the risk of unmatched set, I believe that using many sticks increase the likeliness of encountering the "limits" of the motherboard and trigger incompatibilities with the RAM. Unfortunately I don't have evidence to back this up, but I have had the experience of sticks that all tested fine independently, but failed as a cluster.

If your question was about 2 sticks I'd probably tell you to go ahead and try it, with 8 sticks I'm much more cautious.

RMA considerations

If you run into issue, the RMA process will be much simpler with a matched set. I've had some issues with a new 6 stick matched set a few years back, and had to RMA it 3 times before getting a good one. It would have been troublesome to have 2 independently working products on hand, but failing as a set. Which one is causing problems? What is the chance of exchanging both to fix the issue?

However, you can do solve all those issues that at no cost to you during the return window, and save some money. Whatever you order, make sure to configure them to run at advertised speed, and memtest this seriously. If they work well from the get go, chances are you will be fine for their lifetime.

If a stick later fail under warranty you can RMA that particular set only and pray you get a compatible set in return. But that's only a chance, and much more in the future - so it depends how much you value those savings today.

Underclocking and testing considerations

I think you alluded running them at a slower speed than advertised if you run into issues. That may ease the load and avoid incompatibilities, but figuring out the working configuration is like overclocking - you'll have to do a whole lot of testing to find what frequencies and timings do actually work, if any, and testing 128GB each time is going to take a while. If you settle for frequency and timing that are much lower than needed, you have to consider that the money saved is being eaten away a little by the lower grade of RAM speed you are benefitting from.

TL;DR

For that many sticks and amount of RAM, my personal recommendation would be a matched set. But it's certainly not a bad decision to try it out if you're willing to risk having to go through a return process early on -- and maybe only switch to a matched set if issues do arise.

Answer 2

I've heard stories of mismatched RAM sets. In theory, RAM that is different speeds may work in some cases. In reality, even if that does work in many or even most cases, sometimes there are terrible incompatibilities. In some cases, all the RAM gets detected, but access becomes horrendously slow.

However, if you are getting two identical kits, you should be fine. Especially if you're ordering them from the same place, same model number, same day. Tons of computer systems use two sticks instead of one.

The real big disadvantage to using two sticks instead of one is that if you later decide to get more RAM, you may have all of your RAM slots used up. If you use larger RAM sticks, and so you use fewer sticks, you're less likely to have that problem.

These are old generalizations. It might be that newer technology may change some of these rules. So if you see someone showing evidence that the rules have changed, take heed of that advice. If not, then these old observations may still carry weight.

Answer 3

I've always used multiple single sticks without issue, so having bought a matched set of 4, Gskill Ripjawz and then suffered a DOA ram issue, I would never buy a quad pack again. I would have had to return all 4 sticks for up to a month, for testing and replacement, leaving me with a brand new and dead system, so I just continued on 3 sticks. 4 individual sticks would have allowed me to continue working as the faulty one was replaced. This is the only ram that has ever failed on me, but as the subsequent sticks have failed, I will stick to Crucial, or KIngston from now on.