A new Kepler GPU has started to show up – the GT 645M which is part of the high midrange GPUs of the Kepler series including the GTX 660M, GT 650M (DDR3 and GDDR5), GT 645M, GT 640M and GT 635M.
About the performance difference between GTX 660M and GT 650M we’ve already discussed and here. In short, you can expect about at least 15% advantage of the GTX 660M over the GT 650M GDDR5 averagly and probably something like up to 25%-30% advantage over the GT 650M DDR3 in more taxing scenarios. Also, the GT 650M GDDR5 should have up to 15%-20% advantage over the DDR3 version in specific scenarios – although sometimes it doesn’t have any advantage at all. One more advantage of the GT 650M GDDR5 version is that its high overclockability is backed up by the high memory bandwidth to ensure high gains in performance compared to the DDR3 version.
About the GT 640M and GT 645M. Lets start with some raw specifications:
|Model||Core, shaders (vertex / geometry / pixel)||memory||Core speed|
|GT 640M||Kepler (GK107), 384 unified : 32 : 16, 28nm process||DDR3@900MHZ||625MHZ-709MHZ (depends on manufacturer)|
|GT 645M||Kepler (GK107), 384 unified : 32 : 16, 28nm process||DDR3@900MHZ||710MHZ-780MHZ (at least in this)|
|GT 650M DDR3||Kepler (GK107), 384 unified : 32 : 16, 28nm process||DDR3@900MHZ||835MHZ-950MHZ|
|GT 650M GDDR5||Kepler (GK107), 384 unified : 32 : 16, 28nm process||GDDR5@1000MHZ||735MHZ-850MHZ|
As you can see, the GT 640M, GT 645M and GT 650M DDR3 are actually pretty much the same with a difference in core clocks, plus the GT 650M DDR3 can overclock the core to 950MHZ. So:
- GT 645M vs GT 640M: the GT 645M is roughly 13%-14% faster at least, which is a nice boost if you can get it for the same price as the GT 640M. The new W251EG GT 645M can speed up to 780MHZ (with Turbo-Boost) making it about 10% faster.
- GT 650M DDR3 vs GT 645M: something between 15%-30% difference top with average probably closer to 15%. Examples: Risen 2 (~30%), Skyrim (15%) – taken from here – only one laptop tested and we have to wait for more results, but these numbers will be about the above.
- GT 640M vs GT 635M: already covered. Good 15%-20% advantage (top). Also, the GT 635M is the previous generation Fermi GT 555M which is less power efficient.
So, generally we can say that when moving from each one to the one above (635M -> 640M -> 645M -> 650M DDR3), you gain something around 15% (10%-20%).