CPU-Z says my PC3-10600 1333MHz RAM is actually PC3-10700 667MHz. Do I have 1333 or 667 MHz RAM?

Question

CPU-Z says this:

DDR3
4096 MBytes
PC3-10700 (667 MHz)

I am supposed to have PC3-10600 1333MHz.

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What am I not understanding?

Or, is my RAM only half of what the label and seller claims it to be?

Answer 1

You have 1333 DDR (Double Data Rate) RAM.

The RAM itself runs at 666MHz, but because it is "double pumped" its equivalent data rate is twice that, hence 1333MHz.

Answer 2

You do indeed have PC3-10600. CPU-Z shows only the half of it because DDR RAM like the names says - Double Data Rate - can transfer twice as much data on one I/O bus clock, than the actual IO frequency which CPUZ shows.

If you want to dig deeper in this topic check this link, it describes it really well.