branch prediction

    A technique used in some processors
   with instruction prefetch to guess whether a conditional
   branch will be taken or not and prefetch code from the
   appropriate location.

   When a branch instruction is executed, its address and that of
   the next instruction executed (the chosen destination of the
   branch) are stored in the Branch Target Buffer.  This
   information is used to predict which way the instruction will
   branch the next time it is executed so that instruction
   prefetch can continue.  When the prediction is correct (and it
   is over 90% of the time), executing a branch does not cause a
   pipeline break.

   Some later CPUs simply prefetch both paths instead of trying
   to predict which way the branch will go.

   An extension of the idea of branch prediction is speculative
   execution.

   (1998-03-14)