Microcode: Difference between revisions

Revision as of 21:50, 30 November 2004

Revision as of 16:29, 4 December 2004

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A '''microprogram''' is a program consisting of '''microcode''' that controls the different parts of a computer's central processing unit ([[Central processing unit|CPU]]). The [[memory]] in which it resides is called a [[control store]]. Complex microprograms were typical of [[mainframe computer]]s, such as the [[IBM]] [[System/360]]; but see [[RISC]] for more modern processor design.

Before 1951, the control logic for central processing units was designed by ''ad hoc'' methods. One of the simplest was to use rings of [[flip-flop]]s to sequence the computer's control logic.

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There may also be a [[memory address register]] and a [[memory data register]], used to access the main [[computer storage]].

Together, these elements form an "[[execution unit]]." Most modern [[CPUCentral processing unit|CPUs]]s have several execution units. Even simple computers usually have one unit to read and write memory, and another to execute user code.

These elements could often be bought altogether in one chip. This chip came in a fixed width which would form a 'slice' through the execution unit. These were known a 'bit slice' chips.