What is EU and BIU in 8086?
The correct answer and explanation is :
Execution Unit (EU) and Bus Interface Unit (BIU) in 8086 Microprocessor
The 8086 microprocessor is divided into two main functional units:
- Bus Interface Unit (BIU)
- Execution Unit (EU)
These units work together to ensure efficient instruction execution and memory access.
1. Bus Interface Unit (BIU)
The BIU is responsible for fetching instructions, reading and writing data to memory, and handling input/output operations. It acts as an interface between the processor and memory or I/O devices.
Functions of BIU:
- Instruction Fetching: It prefetches instructions from memory and stores them in the instruction queue (6 bytes FIFO buffer) to improve execution speed.
- Memory and I/O Addressing: It generates memory and I/O addresses using segment and offset registers.
- Bus Control: Controls data transfer between the processor and external memory or I/O devices.
- Address Calculation: Uses segment registers (CS, DS, SS, ES) and offset registers (IP, SI, DI, BP, SP) to calculate the physical address.
2. Execution Unit (EU)
The EU is responsible for executing instructions, performing arithmetic and logic operations, and controlling the flow of program execution. It takes instructions from the BIU and processes them.
Functions of EU:
- Decodes and Executes Instructions: Retrieves instructions from the instruction queue and executes them.
- Performs Arithmetic and Logic Operations: Uses the ALU (Arithmetic and Logic Unit) for calculations.
- Handles Flags and Control Operations: Updates flag registers based on the result of operations.
- Controls Flow of Execution: Manages loops, conditional jumps, and subroutine calls.
Conclusion
In the 8086 microprocessor, the BIU handles communication with memory and I/O devices, while the EU executes instructions and processes data. This pipelining improves performance by overlapping instruction fetch and execution.