Editing Abstract machine (section)

== Implementation ==
Any implementation of an abstract machine in the case of physical implementation (in [[Hardware description language|hardware]]) uses some kind of physical device (mechanical or electronic) to execute the instructions of a [[programming language]]. An abstract machine, however, can also be implemented in [[software]] or [[firmware]] at levels between the abstract machine and underlying physical device.<ref name=":3">{{Citation |last1=Gabbrielli |first1=Maurizio |title=Abstract Machines |date=2010 |url=http://link.springer.com/10.1007/978-1-84882-914-5_1 |work=Programming Languages: Principles and Paradigms |pages=1–25 |place=London |publisher=Springer London |doi=10.1007/978-1-84882-914-5_1 |isbn=978-1-84882-913-8 |access-date=2022-05-16 |last2=Martini |first2=Simone}}</ref> 

* [[Hardware description language|Implementation in hardware]]: The direct implementation of abstract machine in hardware is a matter of using physical devices such as [[Memory cell (computing)|memory]], [[Arithmetic logic unit|arithmetic]] and [[Logic gate|logic circuits]], buses, etc., to implement a physical machine whose machine language coincides with the [[programming language]]. Once constructed, it would be virtually hard to change such a machine.<ref name=":3" /> A [[Central processing unit|CPU]] may be thought of as a concrete hardware realisation of an abstract machine, particularly the [[Processor (computing)|processor's design]].<ref>{{Cite report |last1=Bair |first1=Ray |last2=Chien |first2=Andrew |last3=Cook |first3=Jeanine |last4=Donofrio |first4=Dave |last5=Grider |first5=Gary |last6=Kuehn |first6=Jeff |last7=Moore |first7=Shirley |last8=Shalf |first8=John |last9=Vetter |first9=Jeff |date=2018-02-01 |title=Hardware Evaluation: Abstract Machine Models and Proxy Architectures for Exascale Computing |doi=10.2172/1733300 |osti=1733300 |url=http://dx.doi.org/10.2172/1733300|type=Technical report|publisher=U.S. Department of Energy Office of Scientific and Technical Information}}</ref>

* [[Software|Simulation using software]]: Implementing an abstract machine with software entails writing programmes in a different [[Programming language|language]] to implement the [[Data structure|data structures]] and [[Algorithm|algorithms]] needed by the abstract machine. This provides the most flexibility since programmes implementing abstract machine constructs can be easily changed.<ref name=":3" /> An abstract machine implemented as a software simulation, or for which an [[Interpreter (computing)|interpreter]] exists, is called a [[virtual machine]].<ref name=":0">{{Cite web |title=abstract machine from FOLDOC |url=http://foldoc.org/Abstract+machine |access-date=2021-08-07 |website=foldoc.org}}</ref>

* [[Firmware|Emulation using firmware]]: Firmware implementation sits between hardware and software implementation. It consists of [[microcode]] simulations of [[Data structure|data structures]] and [[Algorithm|algorithms]] for abstract machines.<ref name=":3" /> [[Microcode]] allows a computer programmer to write machine [[Machine code|instructions]] without needing to fabricate [[Electronic circuit|electrical circuitry]].<ref>{{Cite book |last1=Gee |first1=J. |last2=Melvin |first2=S. W. |last3=Patt |first3=Y. N. |title=Proceedings of the 19th annual workshop on Microprogramming |chapter=The implementation of Prolog via VAX 8600 microcode |date=1986 |chapter-url=http://dx.doi.org/10.1145/19551.19538 |pages=68–74 |location=New York, New York, USA |publisher=ACM Press |doi=10.1145/19551.19538|isbn=081860736X |s2cid=3846072 }}</ref>