AMD was particularly fond of selling dual and even tripple core CPUs that were quad core chips with some cores disabled. And people where unclocking these cores

AMD was particularly fond of selling dual and even tripple core CPUs that were quad core chips with some cores disabled. And people where unclocking these cores for profit, because they speculated that AMD disables core for the whole batch even if it was a single unit from it that failed the test, so there could be possibly plenty of good cores disabled along the way.