14 DAY TRIAL // NVIDIA has made some changes to the way CUDA cores are distributed among streaming multiprocessors. The Maxwell architecture shows this, at least in the GM107 GPU.
According to VideoCardz, each SMX unit has 128 CUDA cores in the GM107 GPU, not 192 like in SMX units of Kepler GPUs.
That means that the GM107 has 640 CUDA cores, as previously reported, and that the GTX 750 will not have them all enabled, like on the GTX 750 Ti.
Which means that the rumor about 512 CUDA cores is true too, but only for the non-Ti version of the Maxwell graphics card.
After the GM107 (GM107-400 and GM107-300), NVIDIA will launch cards powered by GM108 chips, plus some stronger 20nm Maxwell units called GM206, the GM204, and the GM200, to replace Kepler GK106, GK104, and GK110. The high-end trio will only be here later this year though (2014).