Dynamic Hardware Prediction

2-bit prediction schemes            To remedy this weakness, 2-bit prediction schemes are often used. In a 2-bit scheme, a prediction must miss twice before it is changed.                 A branch-prediction buffer can be implemented as a small, special “cache” accessed with the instruction address during the IF pipe stage, or as a pair of bits attached to each block in the instruction cache and fetched with the instruction. If the instruction is decoded as a branch and if the branch is predicted as taken, fetching begins from the target as soon as the PC is known. Otherwise, sequential fetching and executing continue. If the prediction turns out to be wrong, the prediction bits are changed.