branch prediction

In computer architecture, a branch predictor is the part of a processor that determines whether a conditional branch in the instruction flow of a program is likely to be taken or not. This is called branch prediction. Branch predictors are crucial in today's modern, superscalar processors for achieving high performance. They allow processors to fetch and execute instructions without waiting for a branch to be resolved.
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<processor, algorithm> A technique used in some processors with instruction prefetch to guess whether a conditional branch will be taken or not and prefetch code from the appropriate location.
When a branch instruction is executed, its address and that of the next instruction executed (the chosen destination of the branch) are stored in the Branch Target Buffer. This information is used to predict which way the instruction will branch the next time it is executed so that instruction prefetch can continue. When the prediction is correct (and it is over 90% of the time), executing a branch does not cause a pipeline break.
Some later CPUs simply prefetch both paths instead of trying to predict which way the branch will go.
An extension of the idea of branch prediction is speculative execution.
(1998-03-14)