Branch Target buffer

What is a Branch Target buffer? Explain how it can be used in reducing bubble cycles in cases of branch misprediction.

Branch misprediction occurs when the CPU mispredicts the next instruction to be executed.
The CPU uses pipelining which allows several instructions to be processed simultaneously. But during a conditional jump, the next instruction to be executed depends on the result of the condition. Branch Prediction tries to guess the next instruction. However, if the guess is wrong, we are penalized because the instruction which was executed must be discarded.
Branch Target Buffer (BTB) reduces the penalty by predicting the path of the branch, computing the target of the branch and caching the information used by the branch. There will be no stalls if the branch entry found on BTB and the prediction is correct, otherwise the penalty will be at least two cycles.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: