Showing papers on "Program counter published in 1968"

Look-ahead control for operation of program loops

Abstract: A look-ahead system for a digital computer is disclosed. This digital computer has programmed instructions stored in and retrievable from a memory. Instruction streams from the memory are passed seriatim through a plurality of instruction registers for processing the instructions. A preliminary decoder senses a look-ahead instruction in the instruction stream and a look-ahead counter responds to the decoding of a look-ahead instruction in the preliminary decoder to establish an index in the look-ahead counter. The index in the look-ahead counter is decremented upon the appearance of each subsequent instruction in the instruction stream at the preliminary decoder. There is a branch decoder which is operable in the instruction processing registers following the preliminary decoder for sensing the conditional branch instruction in the instruction stream. A present address register indicates a present address of the instruction to be processed through the instruction processing registers. A third decoder responds to the contents of the present address register to control the supply of instructions in series to the instruction registers. A branch register responds to predetermined conditions in the present address register and the index in the counter to establish in a look-ahead register an address in the memory for the look-ahead instruction in the instruction stream to control the repeat of the fetch of the look-ahead instruction from memory.

Method for execution of jumps in an instruction memory of a computer

Abstract: A computer system performs a jump instruction routine in a program of sequentially available addressed instructions. A jump instruction which includes an operator part and a variable part is stored in at a given address. When the jump instruction is performed the variable part is used to modify the present address of the jump instruction to establish a return address and also another address to indicate where a subroutine is stored.