difference in RAM speeds

[drdoom]

Is there any significant difference in bandwith between DDR3 on a 256 bit bus and DDR5 on a 128bit bus at the same frequency? Also, I saw that DDR4 modules are ready for desktop computer. Are they not using DDR5 because of cost?

[James]

GDDR3, GDDR4, and GDDR5 are not the same thing as DDR3 and the upcoming DDR4. That is the first thing you should be aware of.

To get total bandwidth, you multiply bus width x number of channels x effective operating speed.

So quad channel fully interleaved memory running at the same speed and bus width would be faster than tri channel. (This example taken from the GTX 670 vs. GTX 660 Ti)