This is generally the result of segregating defective parts of the chip in order to create a stable (albeit less powerful) chip. Some of the chips will be full

This is generally the result of segregating defective parts of the chip in order to create a stable (albeit less powerful) chip. Some of the chips will be fully capable of running with all parts enabled, but in a higher power envelope (this is a guess - but I believe that the fully capable chips most likely to be sacrificed are those that have trouble fitting in the ideal power envelope). I would also imagine that (under some circumstances) chips that are fully functional within the expected power envelope will be artificially limited in order to control levels of stock. The vast majority of chips that are limited in this way will be out of spec, unstable or inoperable when unlocked.