Quite often, a new generation of mobile graphics processors is nothing more than a marketing blitz: for instance, you'll find a GeForce GT 635M is much the same thing as a GT 555M, and the GT 630M and GT 540M are identical in all but name. That's not the case today: Nvidia's launching its first 28nm mobile GPUs, and the company's promising twice the efficiency of its existing 40nm silicon. That may sound rather technical, but it's exciting, too: Nvidia can now build twice the graphics power into the same size machine as last year, or, as we saw in our review of the Acer Aspire Timeline Ultra M3, cram a powerful GPU into a thin laptop that can actually play games.
The new GeForce GT 640M in the Acer laptop can pack quite a punch, but its 384 cores, 625MHz reference clockspeed, and 64GB / sec of memory bandwidth actually only constitute the second rung up the Kepler ladder. The GeForce GT 650M bumps the speed up to 850MHz, and the GeForce GTX 660M adds up to 2GB of faster GDDR5 memory (itself clocked at up to 2GHz) to deliver an additional tier of mid-range performance. How well the Kepler chips perform depends on the actual thermal constraints of your laptop, too, as these chips can dynamically clock themselves depending on the amount of heat the rest of the machine puts out. The very same GT 640M chip can run even faster if it's got better cooling, or if your CPU isn't being simultaneously taxed, but if you stick it in a tiny compressed computer with a red-hot processor it won't do quite as well.
There's also another part you might want to be aware of, the GeForce GT 640M LE, because it's 1.) not as powerful as a regular GT 640M, and also 2.) comes in two different variations. One is a 28nm Kepler part, the other a 40nm Fermi, and there's no good way to distinguish between.
It's worth noting that today isn't all about the new GK107 Kepler architecture, though: the company's also built a brand-new set of 28nm GF117 Fermi chips to round out the low end of the marketplace with the GeForce GT 630M and 620M. Nvidia claims that with a quad-core Intel Core i7 processor, even the new 620M can manage a stable 30FPS framerate in DirectX 11 games like Crysis 2 and Battlefield 3, just so long as they're played at 1366 x 768 resolution and at lowest settings.
Last but not least, Nvidia's got a couple of last-gen 40nm Fermi chips for hefty gaming machines, but old habits seem to die hard: the GeForce GTX 675M and GTX 670M sound like dead ringers for the GTX 580M and GTX 570M they'll likely be replacing. In case you're curious, both the GTX 675M and the GTX 580M have 384 cores, a 620MHz clock, 2GB of GDDR5 memory running at up to 96GB / sec across a 256-bit bus, while the GTX 670M seems like it might be a slight refresh to the GTX 570M with a higher 598MHz clockspeed compared to the earlier 575MHz model.
As always, you'll have to be careful picking your chips because of the confusing naming scheme, especially if you want Kepler-exclusive features like TXAA, but it's still never been a better time to be a laptop gamer.