Editing Central processing unit (section)

===Small-scale integration CPUs===
[[File:PDP-8i cpu.jpg|thumb|CPU, [[magnetic-core memory|core memory]] and [[external bus]] interface of a DEC [[PDP-8]]/I, made of medium-scale integrated circuits]]

During this period, a method of manufacturing many interconnected transistors in a compact space was developed. The [[integrated circuit]] (IC) allowed a large number of transistors to be manufactured on a single [[semiconductor]]-based [[Die (integrated circuit)|die]], or "chip". At first, only very basic non-specialized digital circuits such as [[NOR gate]]s were miniaturized into ICs.<ref>{{cite web |title=1962: Aerospace systems are first the applications for ICs in computers |url=http://www.computerhistory.org/siliconengine/aerospace-systems-are-first-the-applications-for-ics-in-computers/ |publisher=[[Computer History Museum]] |access-date=October 9, 2018 |archive-date=October 5, 2018 |archive-url=https://web.archive.org/web/20181005083606/http://www.computerhistory.org/siliconengine/aerospace-systems-are-first-the-applications-for-ics-in-computers/ |url-status=live }}</ref> CPUs based on these "building block" ICs are generally referred to as "small-scale integration" (SSI) devices. SSI ICs, such as the ones used in the [[Apollo Guidance Computer]], usually contained up to a few dozen transistors. To build an entire CPU out of SSI ICs required thousands of individual chips, but still consumed much less space and power than earlier discrete transistor designs.<ref>{{cite web |title=The integrated circuits in the Apollo manned lunar landing program |url=https://www.hq.nasa.gov/alsj/ic-pg3.html |publisher=National Aeronautics and Space Administration |access-date=October 9, 2018 |archive-date=July 21, 2019 |archive-url=https://web.archive.org/web/20190721173218/https://www.hq.nasa.gov/alsj/ic-pg3.html |url-status=live }}</ref>

IBM's [[System/370]], follow-on to the System/360, used SSI ICs rather than [[Solid Logic Technology]] discrete-transistor modules.<ref>{{cite web|title=System/370 Announcement|url=http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR370.html|website=IBM Archives|access-date=October 25, 2017|date=2003-01-23|archive-date=2018-08-20|archive-url=https://web.archive.org/web/20180820122836/https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR370.html|url-status=dead}}</ref><ref>{{cite web|title=System/370 Model 155 (Continued)|url=https://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155B.html|website=IBM Archives|access-date=October 25, 2017|date=2003-01-23|archive-date=2016-07-20|archive-url=https://web.archive.org/web/20160720234350/http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3155B.html|url-status=dead}}</ref> DEC's [[PDP-8]]/I and KI10 [[PDP-10]] also switched from the individual transistors used by the PDP-8 and KA PDP-10 to SSI ICs,<ref>{{cite web|url=http://homepage.divms.uiowa.edu/~jones/pdp8/models/|title=Models and Options|publisher=The Digital Equipment Corporation PDP-8|access-date=June 15, 2018|archive-date=June 26, 2018|archive-url=https://web.archive.org/web/20180626145311/http://homepage.divms.uiowa.edu/~jones/pdp8/models/|url-status=live}}</ref> and their extremely popular [[PDP-11]] line was originally built with SSI ICs, but was eventually implemented with LSI components once these became practical.