4 ms·

Why did the 8086 have the LOCK prefix? I think of it as being mostly useful in parallel contexts, e.g. lock cmpxchg for an atomic compare and swap. But the 8086

Why did the 8086 have the LOCK prefix? I think of it as being mostly useful in parallel contexts, e.g. lock cmpxchg for an atomic compare and swap. But the 8086 was a single core, single thread processor, and I'd be surprised if it were used in multiprocessor machines. Oh! did it have anything to do with the 8087?

userbinator 3y ago
It was designed with the intention of being used in SMP configurations too, and I believe some industrial control systems were built that way.
- agalunar 3y ago
  Color me surprised! That's very neat. Thanks for answering the question!
- drmpeg 3y ago
  Yes, Intel even had their own bus for this called Multibus. The processor lock signal was connected to the Multibus so that a bus master could lock another boards shared memory for an atomic access.
monocasa 3y ago
In addition to what was said about the viability of SMP, the lock prefix is handy for interrupt safe ops without wholesale disabling interrupts.