An apparatus and method in a pipelined microprocessor for replacing one of
two target addresses in a branch target address cache (BTAC) line. If
only one of the two entries is invalid, the invalid entry is replaced. If
both entries are valid, the least recently used entry is replaced. If
both entries are invalid, the entry is replaced corresponding to the side
of the BTAC, indicated by a global status register, not last written to
with an invalid entry. In one embodiment, the global status is updated
only if a side is written when both entries are invalid. In another
embodiment, the BTAC stores N entries per line, where N is greater than
1. The status register maintains information for determining which of the
N sides is least recently written. The least recently written side is
chosen for replacement.