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I'm confused on how exactly the memory works on it. It x2 16gb sticks to make 32gb's. DDR4 2,666 so 2.6 billion cycles p/second. 2,666 x 8 gives us the 21gb throughput in the "PC4 21300"

So I guess that my confusion is what is the correlation between the 32gb's advertised and the 21gb throughput? what is the difference, or what am I misunderstanding?

I have included a link to Newegg to use as an example. http://www.newegg.com/Product/Product.aspx?Item=N82E16820233853

Thank you

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    You are confusing speed with capacity. Also, you are confusing 'b' (bits) with 'B' (bytes).
    – ChrisInEdmonton
    Commented Mar 8, 2016 at 1:42
  • @ChrisInEdmonton So the 32gb is to indicate how much information can be held at any given time, and the 21gb is to indicate how much information can be transferred per-second? Where am I confusing bits with Bytes?
    – airkeyahguh
    Commented Mar 8, 2016 at 1:45
  • @Ramhound so does this mean that the motherboard would need a minimum throughput of 21gb p/second?
    – airkeyahguh
    Commented Mar 8, 2016 at 3:47
  • Or rather the expansion slot
    – airkeyahguh
    Commented Mar 8, 2016 at 3:49
  • Minimum ratings aren't useful, because your computer will have very little going most of the time. Your memory controller should have a maximum bandwidth that is greater than or equal to your memory's maximum rating. It's not the end of the world if your RAM is faster than your motherboard, because your RAM will be happy to serve up bits just as slowly as your motherboard asks for them. You'll just be leaving potential performance on the table, that's all.
    – picobit
    Commented Mar 8, 2016 at 4:03

2 Answers 2

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Firstly, the annotation GB is not equal to Gb. The first is gigabytes, the second gigabits. Bits typically are used to measure speeds, bytes to measure storage, although that obviously isn't a guarantee as they can be converted, but is the case here.

Unfortunately the term gigabyte is ambiguous, as it can be a decimal or binary calculation. This means in some instances a gigabyte can be either 1000000000 bytes, or 1073741824 bytes. The term gibibyte (GiB) always refers to the latter, and typically RAM manufacturers use this value when referring to capacity.

The RAM in question has a capacity of 32GB in total. This means, however long it takes to do it, it cannot hold more than 32 gigabytes of data at any one time. The throughput is a factor in determining how quickly this data can be accessed.

The maximum throughput will be handled by the memory controller, which may be a feature of the CPU (Core i series for example) or of the chipset on the motherboard northbridge on older boards. For your example, you'd need to check the cpu supported DDR4 2666MHz modules.

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    I really wish that I had my 15 rep so that I could 1up you on this. A fantastic answer and I appreciate it. I am wondering though, these things aside, were my calculations correct or incorrect? If I used GB and Gb accordingly to note the differences between the indicated storage and speed, would everything else be correct? I just want to be sure that I understand this conceptually. Thank you!
    – airkeyahguh
    Commented Mar 17, 2016 at 19:46
  • Well, it is like a sand pit. It has some volume, so you can put only so much sand in it for a certain point in time. But either you can shovel the sand with a small shovel or (mostly when it is built) you just dump a full truck right into it. That is the actual throughput. The physical limit is called bandwidth.
    – AdamKalisz
    Commented Jul 14, 2017 at 13:50
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Well, if you want to understand, read the article here: http://www.anandtech.com/show/6372/memory-performance-16gb-ddr31333-to-ddr32400-on-ivy-bridge-igp-with-gskill

It is very technical, but it covers everything important and doesn't go too deep.

On the latencies associated with DRAM, have a look here: http://pics.crucial.com/wcsstore/CrucialSAS/pdf/en-us-c3-whitepaper-speed-vs-latency-letter.pdf

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