Explain why 8086 internal architure is divided into BIU and EU.

The architecture of 8086 is divided into two functional parts i.e.

(i) Execution unit (EU)

(ii) Bus interface unit (BIU)

These two units work asynchronously.

Functional division of architecture speeds up the processing, since BIU and EU operate parallel and independently i.e., EU executes the instructions and BIU fetches another instruction from the memory simultaneously. As the whole architecture is divided into two independent functional parts and both the subsystem’s operations can be overlapped, hence the architecture is PIPELINING type of architecture.

The execution unit informs the BIU of the processor regarding from where to fetch the instructions from and then executes these instructions. The BIU handles transfer of data and address between the processor and memory /I /O devices by computing address (Physical/ Effective address) and send the computed address to memory / I/ 0 and fetches instruction codes then stores them in FIFO register set called Queue register. The BIU also relocates the addresses of the un relocated operands and reads/writes data from/to memory / I/ O devices.