Editing System request (section)

== History ==

The specific low level function intended for the SysRq key was to switch between operating systems. When the original IBM-PC was created in 1980, there were three leading competing operating systems: [[PC DOS]], [[CP/M-86]], and [[UCSD p-System]],<ref>{{cite web|url=http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html|archive-url=https://web.archive.org/web/20060814072427/http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html|url-status=dead|archive-date=August 14, 2006|title=Original IBM PC Product fact sheet|date=August 12, 1981|publisher=IBM Information Systems Division|access-date=January 13, 2010}}</ref> while [[Xenix]] was added in 1983–1984. The SysRq key was added so that multiple operating systems could be run on the same computer, using the capabilities of the [[Intel 80286|286]] chip in the PC/AT.<ref>Personal interview with Sandy Meade, creator of the SysRq key</ref>{{vc|date=April 2013}}

A special key was needed because most [[software]] of the day operated at a low level, often bypassing the OS entirely, and typically made use of many [[hotkey]] combinations. The use of [[terminate-and-stay-resident]] (TSR) programs further complicated matters. To implement a [[Context switch|task switching]] or [[Computer multitasking|multitasking]] environment, it was thought that a special, separate key was needed. This is similar to the way "[[Control-Alt-Delete]]" is used under [[Windows NT]].

On 84-key keyboards (except the 84-key IBM Model M space saver keyboard), SysRq was a key of its own. On the later 101-key keyboard, it shares a physical key with the [[Print screen]] key function. The [[Alt key]] must be held down while pressing this dual-function key to invoke SysRq. This continues through modern PC keyboards.<ref name="modern">{{cite web|title=What Are the Sys Rq, Scroll Lock, and Pause Break Keys on My Keyboard?|date=26 September 2016 |access-date=March 2, 2020|url=https://www.howtogeek.com/125315/htg-explains-what-are-the-sys-rq-scroll-lock-and-pausebreak-keys-on-my-keyboard/}}</ref>

The default BIOS keyboard routines simply ignore SysRq and return without taking action. So did the [[MS-DOS]] input routines. The keyboard routines in [[Library (software)|libraries]] supplied with many high-level languages followed suit. Although it is still included on most PC keyboards manufactured, and though it is used by some{{which|date=July 2019}} debugging software, the key is of no use for the vast majority of users.

On the [[Hynix|Hyundai/Hynix]] Super-16 computer, pressing {{key press|Ctrl|SysRq}} will hard boot the system (it will reboot when {{key press|Ctrl|Alt|Del}} is unresponsive, and it will invoke startup memory tests that are bypassed on soft-boot).{{Fact|date=January 2008}}