Short Answer

The instruction queue in 8086 is a small memory area inside the processor that stores upcoming instructions before they are executed. It helps in improving the speed of processing.

In simple words, the instruction queue allows the processor to fetch instructions in advance while executing current instructions. This reduces waiting time and increases overall performance using a technique called pipelining.

Detailed Explanation:

Instruction queue in 8086

The instruction queue in 8086 microprocessor is an important feature that helps in increasing the speed of instruction execution. It is a temporary storage area inside the Bus Interface Unit (BIU) where instructions are stored before they are executed by the Execution Unit (EU). The instruction queue in 8086 can hold up to 6 bytes of instructions.

The main purpose of the instruction queue is to allow parallel processing. While the Execution Unit is busy executing one instruction, the Bus Interface Unit fetches the next instructions from memory and stores them in the queue. This reduces idle time and improves efficiency.

Role in pipelining

The instruction queue is a key part of the pipelining process in the 8086 microprocessor. Pipelining means performing multiple operations at the same time in different stages.

In the 8086, pipelining is achieved by dividing tasks between the BIU and EU. The BIU fetches instructions and fills the queue, while the EU decodes and executes instructions from the queue. Because of this, instruction fetching and execution happen simultaneously.

This overlap of operations increases the speed of the processor and makes it more efficient compared to earlier processors like the 8085.

Working of instruction queue

The instruction queue works continuously during program execution. The BIU fetches instruction bytes from memory and places them into the queue. The EU takes instructions from the front of the queue, decodes them, and executes them.

As the EU removes instructions from the queue, the BIU keeps adding new instructions. This ensures that the queue is always filled as long as there are instructions to fetch.

If a branch instruction occurs, such as a jump or call, the queue is cleared because the next instructions will come from a different memory location. After that, the BIU starts filling the queue again with new instructions.

Advantages of instruction queue

The instruction queue provides several advantages. It reduces the time required to fetch instructions because fetching is done in advance. This leads to faster execution of programs.

It also improves the efficiency of the processor by allowing parallel operation of different units. The use of pipelining increases overall system performance.

Another advantage is better utilization of system resources, as both BIU and EU can work simultaneously without waiting for each other.

Limitations of instruction queue

Although the instruction queue improves performance, it has some limitations. If there is a jump or branch instruction, the queue must be cleared, which causes a small delay.

Also, the queue has a limited size of 6 bytes, so it cannot store a large number of instructions. Despite these limitations, it still significantly improves performance.

Conclusion

The instruction queue in the 8086 microprocessor is a small storage area that holds instructions before execution. It enables pipelining by allowing instruction fetching and execution to occur simultaneously. This improves speed and efficiency, making the 8086 more powerful than earlier processors.