80386

After introduction of the 386 into the market the first CPUs had been provided with a bug in the 32 bit MUL instruction ("MUL bug") which prevented running the chip in protected mode. Those chips were marked "only s/w 16 bits" or with a single sigma and were only sold to OEP. The tested and passed chips carry a double sigma on the package. Nevertheless the 16-bit 80386 was much faster than previous chips and none of the applications required protected mode so Intel didn't feel obliged to pronounce the bug. Unlike the first Pentium 60 with its fdiv bug Intel did not offer an exchange for enhanced versions.