The two-bit predictor scheme uses only the recent behavior of a single branch to predict the future of that branch.
Correlations between different branch instructions are not taken into account.
The correlation-based predictors or correlating predictors are branch predictors that additionally use the behavior of other branches to make a prediction.
While two-bit predictors use self-history only, the correlating predictor uses neighbor history additionally.
Notation: (m,n)-correlation-based predictor or (m,n)-predictor uses the behavior of the last m branches to choose from 2m branch predictors, each of which is a n-bit predictor for a single branch.
Branch history register (BHR): The global history of the most recent m branches can be recorded in a m-bit shift register where each bit records whether the branch was taken or not taken.