In this paper we implement several basic operating system primitives by using a "replace-add" operation, which can supersede the standard "test and set", and which appears to be a universal primitive for efficiently coordinating large numbers of independently acting sequential processors. We also present a hardware implementation of replace-add that permits multiple replace-adds to be processed nearly as efficiently as loads and stores. Moreover, the crucial special case of concurrent replace-adds updating the same variable is handled particularly well: If every PE simultaneously addresses a replace-add at the same variable, all these requests are satisfied in the time required to process just one request.

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He joined IBM in 1955 and over a ten year tenure there, worked principally in theareas ofcircuit development and computer organization and design. He was a designer and manager ofprototype versions oftheIBM 7090and 7094/11 and laterwas the nianager responsible for design and development of the System 360 Model 91 Central Processing Unit. He was a member ofthe faculty of Northwestern University andThe