Matched sets of RAM vs 2 different buys at different times?


Feb 1, 2006
I read that some RAM manufacturers suggest buying a "matched and tested" set of RAM, for instance 4 sticks of 4 gigs for 16 gigs (4 X 4) of RAM vs 2 different sets of 8 gigs (2 X 4) (Same model, same Manf., same timings, etc).

Is this true or does it really matter that much? Of course you pay a premium for a "matched" set over the 2 different sets.

For instance 2 sets of this: vs one set of this:

Anybody here have experience with matched sets or 2 different sets?

And if anybody here has the time, can you educate this old fart with a simple explanation of what different timings mean? For instance, what's the difference between 7-10-10-28, 8-8-8-24 and 9-9-9-24? Is one "better" or faster?

Thanks all.


In regards to you first inquiry, the matched set provides greater chance of stability, but also removes one more possibility if the system becomes unstable. For example: Using the 16 GB kit means that these sticks have come from the same lot; were tested to work with each other; and as a result, removes compatability issues from the table.

On the other hand, if you were to buy to sets of 8GB kits at different times and find your system unstable, you now have one more possibility to explore. The possibility is whether or not the sticks are compatible with each other. You see, there is more to RAM than just "the big 4"(CAS, tRCD, tRP, tRAS).

Now, that isn't to say that you can't use different kits simultaneously; however, some motherboards tend to be picky about this issue. When in doubt, just use something from the motherboard Quality/Qualified Vendor List, as this list will show what products have been tested to be compatible.

So, in short, it is always best to install kits when you want more than one stick of RAM.

In regards to the timing, the numbers represent clock cycles. Let's take your first set. 7-10-10-28 means that CAS = 7 clock cycles, tRCD = 10, tRP = 10, tRAS = 28. A clock cycle is the time any data access command takes to process. The lower numbers in the timing sequence means that the latency is lower. Better and/or faster is not apparent unless you consider the frequency of the RAM as well.

For example: 8-8-8-24 vs 9-9-9-24; clearly the faster one is CL8, but only if the frequency is the same. So instead, consider comparing the RAM like this:

DDR3 2000 CL8 is faster than DDR3 2000 CL9