ALU

(Arithmetic Logic Unit) The high-speed CPU circuit that does calculating and comparing. Numbers are transferred from memory into the ALU for calculation, and the results are sent back into memory. Alphanumeric data are sent from memory into the ALU for comparing. The results are tested by GOTOs; for example, IF ITEMA EQUALS ITEMB GOTO UPDATE ROUTINE.

Some chips have multiple ALUs that allow for simultaneous calculations. For example, Chromatic Research's Mpact media processor chip had 450 of them. It allowed audio, video and other multimedia processes to be performed simultaneously. See control unit and Mpact chip.

An ALU in 1957

This was an arithmetic logic unit you sit back and admire. It was part of Honeywell's Datamatic 1000 computer. (Image courtesy of Honeywell, Inc.)

Thirty Years Later

The ALU embedded within this 386 chip would fit on the end of a pencil eraser with room to spare. (Image courtesy of Intel Corporation.)

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