1.9 Performance
In an effort to keep the execution units busy, the processor predicts branches and speculatively executes instructions along the predicted path. When the branch is predicted correctly, this significantly improves performance: for typical programs, branch prediction is 85% to 90% correct. When a branch is mispredicted, the processor must discard instructions which were speculatively fetched and executed. Usually, this effort uses resources which otherwise would have been idle, however in some cases speculative instructions can delay previous instructions.
