Digital Equipment Corporation

John C Manton

Kenneth Alan Okin

William F Bruckert

Tryggve Fossum

Alfred J Dellicicchi

Richard E Glackemeyer

Allan E Helenius

Anthony N Zacconi

John A DeRosa, Jr

A central processor unit for a digital data processing system that processes prefetched instructions including a conditional branch instruction. The processor includes a fetch unit that has separate portions, one that retrieves operands and the other that retrieves instructions. When the fetch unit fetches a conditional branch instruction, it may continue to prefetch 'branch not taken' instructions using the instruction fetch portion. The fetch unit initially uses the operand fetch portion to prefetch 'branch taken' instructions. If it is determined that the branch is not taken, the prefetch operation is aborted, otherwise the prefetch operation is allowed to continue to provide the next instruction used by the processor.

Instruction prefetch system for conditional branch instruction for

In a data processing system, a memory (32) consists of data words and associated error-correction codes that are independently accessible; it is possible simultaneously to read a data word and write its associated error-correction code. This allows a memory-control circuit (30) immediately to store in the memory (32) a data word sent by a processor (10) while it is concurrently in the process of generating the error-correction code for that data word. The result is that the memory-control circuit (30) can subsequently fetch the newly stored data word before storage of its associated error-correction code is complete. This reduces delays involved in error-correction-code generation. The data word includes not only non-redundant information but also parity bits that both the processor (10) and the memory-control circuit (30) employ to determine whether a data word is correct. If the memory-control circuitry (30) determines that a word that it has forwarded to the processor (10) is incorrect, it immediately fetches the corresponding error-correction code and corrects the location in memory. Then, when the processor (10) finds that the parity is incorrect in the data word, it repeats its request for the data word in question, which the memory-control circuit (30) has corrected in the memory (32).

Pipeline error correction

A memory unit connected in a data processing system including a central processor unit and an input/output unit. The memory unit is connected to the central processor unit through one port, and to the input/output unit through a second port. When the central processor unit wants to transfer data with the input/output unit, it does so through the memory unit.

Two-port memory controller

A memory unit for connection in a data processing system in which the central processor unit may transfer data to or retrieve data from portions of two storage locations in one transfer. The memory unit has a data rotating and storage network that rotates the data and stores it as necessary for its transfer to or from the addressed storage locations.

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Marlboro, MA, United States of America

John C Manton