The second major issue discussed is the question of what information to store in the BTB. A BTB entry can consist of one or more of the following: branch tag (i.e. the branch address), prediction information, the branch target address, and instructions at the branch target. A variety of BTB designs, with one or more of these fields, are evaluated and compared. This study is then extended to multilevel BTBs, in which different levels have different amounts of information per entry. For the specific implementation assumptions used, multilevel BTBs improved performance over single level BTBs only slightly, at the cost of additional complexity. Multi-level BTBs may provide significant performance improvements for other implementations, however.
Design target miss ratios for BTBs are also developed, so that the performance of BTBs for real workloads may be estimated.