Closely coupled configuration-

1. Co-processor cannot take control of the bus; it does everything through the CPU.
2. 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.

1. Two 8086’s cannot be closely coupled.