LOCK             Lock the Bus                        Flags: not altered

LOCK

LOCK is a one-byte prefix that can precede any instruction. LOCK
causes the processor to assert its bus lock signal while the
instruction that follows is executed. If the system is configured such
that the LOCK signal is used, it prevents any external device or event
from accessing the bus, including interrupts and DMA transfers.

                                                                          
Operands                  Clocks   Transfers  Bytes   Example
no operands                 2          -        1     LOCK XCHG FLAG,AL
                                                                          

Note:          This instruction was provided to support multiple
processor systems with shared resources. In such a
system, access to those resources is generally
controlled via a software-hardware combination using
semaphores.

This instruction should only be used to prevent
other bus masters from interrupting a data movement
operation.  This prefix should only be used with
XCHG, MOV, and MOVS.

See also: HLT
See also: WAIT
See also: ESC

LOCK Lock the Bus