Editing History of computing hardware (section)

===Microprogramming===
In 1951, British scientist [[Maurice Wilkes]] developed the concept of [[microcode|microprogramming]] from the realisation that the [[central processing unit]] of a computer could be controlled by a miniature, highly specialized [[computer program]] in high-speed [[Read-only memory|ROM]]. Microprogramming allows the base instruction set to be defined or extended by built-in programs (now called [[firmware]] or [[microcode]]).{{sfn|Horowitz|Hill|1989|p=743}} This concept greatly simplified CPU development. He first described this at the [[University of Manchester]] Computer Inaugural Conference in 1951, then published in expanded form in ''[[IEEE Spectrum]]'' in 1955.{{citation needed|date=April 2013}}

It was widely used in the CPUs and [[floating-point]] units of [[mainframe computer|mainframe]] and other computers; it was implemented for the first time in [[EDSAC 2]],<ref name="edsac2">{{Cite journal |last1=Wilkes |first1=M. V. |author-link1=Maurice Wilkes| title=Edsac 2 |doi=10.1109/85.194055 |journal=IEEE Annals of the History of Computing| volume=14 |issue=4 |pages=49–56 |year=1992 |s2cid=11377060}}</ref> which also used multiple identical "bit slices" to simplify design. Interchangeable, replaceable tube assemblies were used for each bit of the processor.{{efn|The microcode was implemented as ''extracode'' on Atlas.<ref>{{cite web |title=The Atlas Supervisor |author1=T. Kilburn |author2=R. B. Payne |author3=D. J. Howarth |year=1962 |work=Atlas Computer |url=https://www.chilton-computing.org.uk/acl/technology/atlas/p019.htm |access-date=2010-02-09 |archive-date=2009-12-31 |archive-url=https://web.archive.org/web/20091231062425/http://www.chilton-computing.org.uk/acl/technology/atlas/p019.htm |url-status=live }}</ref>}}