Cpu Design Questions Medium
The branch target buffer (BTB) is a component in a CPU that helps improve the performance of branch instructions. Its main role is to predict the target address of a branch instruction before it is actually executed.
When a branch instruction is encountered, the CPU needs to determine whether the branch will be taken or not, and if taken, it needs to know the target address to which the program flow will be redirected. This prediction is crucial for maintaining the pipeline efficiency and avoiding pipeline stalls.
The BTB stores the history of branch instructions and their corresponding target addresses. It works by associating the branch instruction's address with the predicted target address in a table-like structure. When a branch instruction is encountered, the BTB is consulted to check if there is a prediction available for that particular branch.
If a prediction is found in the BTB, the CPU can fetch the instructions from the predicted target address, allowing the pipeline to continue execution without waiting for the branch instruction to be fully resolved. This technique is known as branch prediction.
However, if the prediction in the BTB turns out to be incorrect, the CPU needs to discard the fetched instructions and restart the pipeline from the correct target address. This is called a branch misprediction, and it can result in a performance penalty.
Overall, the role of the BTB is to improve the performance of branch instructions by predicting their target addresses. By doing so, it helps reduce the number of pipeline stalls and allows the CPU to fetch and execute instructions more efficiently.