Final answer:
A branch-target buffer (BTB) is a cache that stores the predicted target addresses of branch instructions. It helps reduce the branch penalty by allowing the processor to fetch instructions from the predicted target address without waiting for the branch to be resolved.
Step-by-step explanation:
A branch-target buffer (BTB) is a cache that stores the target addresses of conditional and unconditional branch instructions in a computer program. It helps reduce the branch penalty, which is the delay caused by a conditional branch instruction that needs to be resolved.
When the processor encounters a branch instruction, the BTB stores the predicted target address of the branch. If the prediction is correct, the processor can fetch instructions from the predicted target address without waiting for the branch to be resolved, thus reducing the branch penalty.
For example, let's say a branch instruction is encountered that branches to instruction B if a certain condition is met and otherwise branches to instruction C. If the BTB predicts that the condition will be true and the program actually takes the branch to instruction B, the processor can immediately fetch instructions from instruction B, avoiding the branch penalty.