 A historical use of has been to assist in patching PROMs when bugs were discovered in a system's firmware.A typical technique often used during firmware development was to arrange for the vector to point to an unprogrammed "patch area" in the PROM.In the event a bug was discovered, patching would be accomplished by "blowing" all of the fuses at the address where the faulty instruction was located, thus changing the instruction's opcode to .