Definition
2-Bit Branch Predictor
A 2-bit branch predictor is an [[Knowledge/n-Bit Branch Predictor|-bit branch predictor]] with , giving four states: strongly not taken (00), weakly not taken (01), weakly taken (10), and strongly taken (11).
The prediction is not taken in states 00 and 01, and taken in states 10 and 11. Because the counter saturates, a single anomalous outcome cannot reverse a strong prediction — it only weakens it. Two consecutive opposite outcomes are needed to flip the prediction direction.
This is the most common practical predictor width. The 2-bit saturating counter fixes the oversensitivity of the 1-bit predictor while remaining cheap to implement.