One 8 GB DIMM vs two 4 GB DIMMs in dual channel mode

Question

Is one 8 gigabyte DIMM faster or slower or the same as two 4 gigabyte DIMMs in dual channel mode? This is DDR3-1333.

Solution

It depends.

Assuming equally fast DIMMs (just 1333 does not say much, only that it works at 667 MHz), then dual channel mode is on average about 5% faster.

This will vary per application. E.g. a scientific program which multiplies two large matrixes (too large to fit into a cache) will see a much bigger boost. A program which does not access memory much, or one which is GPU bound will barely see any improvement.

Single vs dual channel RAM tests on Toms Hardware

If you use a motherboard on a modern Intel setup then using on DIMMs means that you will be able to move two DIMMs later on without sacrificing speeds. (more than 2 DIMMs, or more than 4 ranks usually slows down memory access on Intel by moving to a 2T command phase).

Comments

[ganesh]

I disagree. That question is about "is it better to have more RAM and single channel, or less RAM and dual channel?" This is about equal amounts of memory.

[Peleus]

No Sirex, this is purely is it better to have it dual channel or single channel - not "more".

[ganesh]

Yes, but the question is two 4 GB DIMMs (total 8 GB) vs one 8 GB DIMM (same 8 GB total).