Microcode: Difference between revisions

Revision as of 21:21, 5 July 2025

Revision as of 16:24, 17 July 2025

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{{Program execution}}

In [[processor design]], '''microcode''' serves as an intermediary layer situated between the [[central processing unit]] (CPU) hardware and the programmer-visible [[instruction set architecture]] of a computer.<ref name="Kent2813">{{cite book |last1=Kent |first1=Allen |url=https://books.google.com/books?id=EjWV8J8CQEYC |title=Encyclopedia of Computer Science and Technology: Volume 28 - Supplement 13 |last2=Williams |first2=James G. |date=April 5, 1993 |publisher=Marcel Dekker, Inc |isbn=0-8247-2281-7 |___location=New York |pages=34 |access-date=Jan 17, 2016 |archive-url=https://web.archive.org/web/20161120161636/https://books.google.com/books?id=EjWV8J8CQEYC |archive-date=November 20, 2016 |url-status=live}}</ref>{{Page needed|date=July 2022}} It consists of a set of hardware-level instructions that implement the higher-level [[machine code]] instructions or control internal [[finite-state machine]] sequencing in many [[digital processing]] components. While microcode is utilized in [[Intel]] and [[AMD]] general-purpose CPUs in contemporary desktops and laptops, it functions only as a fallback path for scenarios that the faster [[hardwired control unit]] is unable to manage.<ref name="FogMicro">{{cite report |url=https://www.agner.org/optimize/microarchitecture.pdf |title=The microarchitecture of Intel, AMD and VIA CPUs |last1=Fog |first1=Agner |date=2017-05-02 |publisher=Technical University of Denmark |access-date=2024-08-21 |archive-url= https://web.archive.org/web/20170328065929/https://agner.org/optimize/microarchitecture.pdf |archive-date=2017-03-28 |url-status=live}}</ref>

Housed in special high-speed memory, microcode translates machine instructions, [[state machine]] data, or other input into sequences of detailed circuit-level operations. It separates the machine instructions from the underlying [[electronics]], thereby enabling greater flexibility in designing and altering instructions. Moreover, it facilitates the construction of complex multi-step instructions, while simultaneously reducing the complexity of computer circuits. The act of writing microcode is often referred to as ''microprogramming'', and the microcode in a specific processor implementation is sometimes termed a ''microprogram''.