Originally Posted by Arni90
Is there something that doesn't make sense about it?
It's not like there needs to be a specific ratio of say 2 SMXes per 8 ROPs/64-bit memory bus.
It don't need, but it should have symmetric design, at least on the flag chip. 5 SMX/3 clusters is strange.
So I did some calculation, and found a possible way how can they do that. Basically they would do something like it has been done with PS3 Cell, it was printed with 8 CPUS, but released with 7. (6 usable for programmers)
They will print 6 SMX, and then test them. When all 6 would work, they would disable one, because 660 has 960 cores. (They can also keep it, and later decide to release it as GTX 660-1152.) When one of these 6 SMX will not work, they would erase it by LASER, and have correct specification to release it as GK106-400.
When manufacturing defect would affect two clusters each on a different memory controller, they would erase them and release it as GK106-250.
Now when manufacturing defect would affect memory controller/ROP cluster, or both affected clusters would be on the same controller, they would erase memory controller and both SMX connected to it, and they would release it as GK106-200.
cluster defects: 0 1 2
controller defects 0 GK106-400 GK106-400 GK106-250/GK106-200 (2/3 to 1/3 ratio)
1 GK106-200 GK106-200 GK106-200
But it seem strange: There are lot of GK106-400, which is correct, they did it to massively improve production rate of GK106-400. There are lot of GK106-200, majority of which can go to OEM. However there are just few of GK106-250. (Of course memory controller defects would be rare, thus the above table isn't exactly symmetric.)
The die size, 221 mm^2, actually supports the 6 SMX printed, 5 healthy SMX kept idea. They will pay for it by using about 1/8 - 1/6 more on wafer, but it would considerably improve yields.
If they went this way, then GK106-200 would have 768 CUDA cores, and it would basically behave as a GT 640, just it would be twice as fast... (GT 640 had great scores in Diablo 3, thus GK106-200 would be great Diablo 3 card. Of course it would be bandwidth starved as hell.) The numbering GK106-200 and GK106-250 also suggest they only changed number of ROP and memory controllers, the rest of the chip remained the same.Edited by Raghar - 9/6/12 at 9:22am