What is out of order execution in computer architecture?
Answers
Out-of-order Execution
A processor that executes the instructions one after the other, may use the resources inefficiently that leads to poor perfpormance of the processor.To improve the performance of the processor this can be done in two ways. By executing different sub-steps of sequential instructions simultaneously or even executing the instructions entirely simultaneously. Further improvement in the processor can achieved through out-of-order execution. Out-of-order execution can be achieved by executing the instruction in an different from the original order they appear.
Out-of-order execution is an approach that is used in high performance microprocessors.This approach efficiently uses instruction cycles ( is a process by which a computer retrieves program instruction from its memory, determines what action the instruction requires and carries out those actions. and reduces costly delay. A processor will execute the instructions in an order of availability of data or operands instead of original order of the instructions in the program.By doing so the processor will avoid being idle while data is retrieved for the next instruction in a program.
In other words, processor that uses multiple execution units completes the processing of instructions in wrong order. For example, I-1 and I-2 are the two intructions where I-1 comes first then I-2. In the out-of-order execution, a processor can execute I-2 instruction before I-1 instruction has been completed. This flexibility will improve the performance of the processor since it allows execution with less waiting time.