Remember the GeForce4 MX? The low-end GPU was pretty forgettable, to be honest, but Nvidia is bringing back the MX moniker for handful of new mobile GPUs. Instead of being budget offerings, these new parts start at the high end of the mobile GeForce lineup. The fastest of the three is the GeForce GTX 680MX, which is the first mobile GPU to offer Kepler's full payload of 1536 shader ALUs. The previous top-of-the-line model, the GTX 680M, has only 1344 ALUs.
The two mobile 680s share the same 720MHz core clock, down considerably from Kepler's 1GHz+ clock speed on the desktop. Nvidia has ramped up the MX's memory speed by quite a bit, though. While the 680M's GDDR5 memory runs at 3.6 GT/s, the MX's RAM clocks in at 5 GT/s. That's only 1 GT/s short of desktop GTX 680 parts.
One step down the line, the GeForce GTX 675MX improves upon the 675M. The new chip has 960 ALUs, more than doubling the 384 ALUs in its predecessor. The 675MX's 600MHz core clock has been dialed back by 20MHz, but the memory speed has been increased by 600 MT/s. A similar story plays out with the GeForce GTX 670MX, which has more ALUs and a higher memory speed than the old 670M.
We haven't seen any new notebooks announced with these MX GPUs, but Nvidia points out that the GeForce GTX 680MX and 675MX will be available as options on Apple's new 27" iMac. According to the Apple Store, that system won't start selling until December. When it arrives, the new 27" iMac could be the most potent all-in-one gaming system around. The market for all-in-one systems is growing at a much faster rate than the one for traditional desktops, which means we could see a lot more mobile GPUs moonlighting outside of notebooks. Thanks to EXPreview for the tip.