A branch target buffer (BTB) is a cache that stores the target address of previously executed conditional and unconditional branch instructions. It is used to predict the target of a conditional or unconditional branch instruction and help improve the performance of pipelined processors by reducing stall cycles caused by branch instructions. When the processor fetches an instruction, it checks the BTB to determine if the instruction is a branch and if so, it predicts the target address based on the previous execution of similar branches. If the prediction is correct, the pipeline continues to execute instructions without any delay. If the prediction is incorrect, the pipeline must be flushed and restarted. The BTB usually has limited capacity and may use various algorithms to determine which entries to evict to make room for new entries.
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