Editing Branch predictor (section)

===Global branch prediction===
A global branch predictor does not keep a separate history record for each conditional jump. Instead it keeps a shared history of all conditional jumps. The advantage of a shared history is that any [[correlation]] between different conditional jumps is part of making the predictions. The disadvantage is that the history is diluted by irrelevant information if the different conditional jumps are uncorrelated, and that the history buffer may not include any bits from the same branch if there are many other branches in between. It may use a two-level adaptive predictor.

This scheme is better than the saturating counter scheme only for large table sizes, and it is rarely as good as local prediction. The history buffer must be longer in order to make a good prediction. The size of the pattern history table grows [[exponential function|exponentially]] with the size of the history buffer. Hence, the big pattern history table must be shared among all conditional jumps.

A two-level adaptive predictor with globally shared history buffer and pattern history table is called a "gshare" predictor if it [[XOR gate|xors]] the global history and branch PC, and "gselect" if it [[concatenation|concatenates]] them. Global branch prediction is used in [[Advanced Micro Devices|AMD]] processors, and in Intel [[Pentium M]], [[intel core|Core]], [[Intel core 2|Core 2]], and [[Silvermont]]-based [[Intel Atom|Atom]] processors.