1. A program instruction flow prediction apparatus for a data processing system having means for prefetching an instruction, said flow prediction apparatus comprising a flow prediction storage element, an instruction storage element containing program instructions to be executed, means coupled with said instruction storage element for addressing an instruction in said instruction storage element, means coupled with said flow prediction storage element and with said addressing means for reading a flow control word in said flow prediction storage element at a location derived from the location of said addressed instruction in said instruction storage element, said flow control word containing at least a branch control portion for predicting the flow of program instructions and a next program instruction address portion containing at least a portion of a next program address if a program branch is predicted, and said addressing means including means for normally employing a next sequential instruction location for use in fetching a next instruction, and for responding to said branch control portion for deriving from said next program instruction address portion a branch location for use in fetching said next instruction, said branch location being used in lieu of said next sequential instruction location.