They use something called an eFUSE. It's basically like a fuse that you can blow electronically after the chip has been manufactured. The fuses will disable the cores and disconnect them from the rest of the chip. As to why it was done, there ar... read more
Instead of discarding them, you disable two of the 8 cores, and sell them as a 6-core processor. The customer gets a high performance chip, you get two models of processors out of one process, and you lose less chips, so your losses are lower that way. read more