NVIDIA's GeForce GTX 680 graphics card will forever be the star attraction of the 600 series, but the company has now provided some models that consumers will never be able to buy directly.
Instead, the newest video boards are made for OEMs (original equipment manufacturers), who will utilize them in their upcoming desktop systems.
There is a GeForce GT 630, three different GT 640 and the GT 645. Three of them are 28nm-based Kepler cards and the other are rebranded, 40nm Fermi.
That's right, NVIDIA deliberately made its card lineup so complicated that it will be hard to know exactly what you're in for.
For the sake of some coherence, we'll first look at the boards that aren't weirdness embodied, so we'll start with the GeForce GT 630.
Based on the GK107 Kepler GPU, it has 32 texture units, 16 ROPs, 384 CUDA cores and a GPU clock speed of 875 MHz. The DDR3 memory will be of 1 or 2 GB (clock of 891 MHz actual / 1,782 MHz effective).
Physically, the 630 is pretty small, with a low-profile PCB and a small fan cooler. DVI, HDMI and D-Sub connectors exist. The TDP is 50W.
The GeForce GT 645 is a Fermi-based adapter (rebranded GTX 555 apparently), said to have 128-bit memory interface, but probably equipped with 192-bit. The GTX 555 has that much, meaning that NVIDIA's website probably slipped a typo there.
288 CUDA cores, 776 MHz GPU clock, 1 GB GDDR5 VRAM are the specs.
And now we get to the weird part: the supposedly “high-end' GTX 640 is based on the GK107 Kepler, but has the CUDA core count, ROPs and texture units the same as on the GT 630 board. The 950 MHz clock is its only saving grace.
Unfortunately, this doesn't explain why the base GT 640 model is identical to the GT 630 but with a GPU clock that is actually slower (797 MHz). Add to that the higher TDP (75W on all three) and more questions appear instead of answers.
Finally, the wall of weird is completed by the “middle” GT 640, powered by the Fermi GF116. This board has 144 CUDA cores, 24 texture units, 16 ROPs, 720 MHz GPU clock and 1.5 GB or 3 GB of DDR3 at 891 MHz (interface is 192 bits).
may or may not dispel your bafflement. Peruse the new product pages at your discretion.