Multiprocessor systems refer to the use of multiple processors that execute instructions simultaneously and communicate using mailboxes and semaphores. Maximum mode of 8086 is designed to implement 3 basic multiprocessor configurations:

1. Co-processor (8087)
2. Closely coupled (dedicated I/O processor: 8089)
3. Loosely coupled (Multi-bus)
4. Co-processors and closely coupled configurations are similar - both the CPU and the external processor share:
5. Memory
6. I/O system
7. Bus & bus control logic
8. Clock generator

Closely coupled configuration-

Co-processor cannot take control of the bus; it does everything through the CPU.

Closely Coupled processor may take control of the bus independently 8089 shares CPU’s clock and bus control logic.

Communication with host CPU is by way of shared memory.

Host sets up a message (command) in memory.

Independent processor interrupts host on completion.

Two 8086’s cannot be closely coupled.