Microcode: Difference between revisions

Revision as of 16:31, 25 January 2006

Revision as of 21:08, 2 March 2006

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== The reason for microprogramming ==

Microprogramming was originally developed as a simpler method of developing the control logic for a computer. As logic design techniques improved, this reason declined in importance, but other reasons became more important.

When computers were first developed, the speed of the central processor approximately matched the speed of the main memory, and each instruction word read from memory could efficiently command the execution of a single operation by the central processing unit. As logic design became more advanced, however, it became possible for the central processor to execute operations much faster than instruction words could be fetched from memory.

Microprogramming was a response to this imbalance. By allowing each instruction fetched from memory to invoke a micro[[subroutine]], instructions fetched from memory could command the central processor to perform very complex operations such as the addition of floating-point numbers or the execution of complete operations on character strings. The rise of [[CISC]] computers was a direct result of the availability of microprogramming and many computer architectures such as the [[IBM]] [[System/360]] and the [[Digital Equipment Corporation|DEC]] [[VAX]] family used complex microprograms.

In recent times, advances in memory speeds, especially [[cache memory]], have made microprogramming less necessary, leading to the return of direct-execution computer architectures. (now calledNote that [[RISC]]). is not the same as direct execution, though the techniques often are found together.

== Other benefits ==