System Request (SysRq or Sys Req) is a key on personal computerkeyboards that has no standard use. Introduced by IBM with the PC/AT, it was intended to be available as a special key to directly invoke low-level operating system functions with no possibility of conflicting with any existing software. A special BIOS routine – software interrupt 0x15, subfunction 0x85[1] – was added to signal the OS when SysRq was pushed or released. Unlike most keys, when it is pressed nothing is stored in the keyboard buffer.
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,[2] 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 286 chip in the PC/AT.[3][unreliable source?]
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 task switching or 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.[4]
The default BIOS keyboard routines simply ignore SysRq and return without taking action. So did the MS-DOS input routines. The keyboard routines in 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?] debugging software, the key is of no use for the vast majority of users.
On the Hyundai/Hynix Super-16 computer, pressing Ctrl+SysRq will hard boot the system (it will reboot when Ctrl+Alt+Del is unresponsive, and it will invoke startup memory tests that are bypassed on soft-boot).[citation needed]
Microsoft has also used SysRq for various OS- and application-level debuggers. In the CodeView debugger, it was sometimes used to break into the debugging during program execution.[6] For the Windows NT remote kernel debugger, it can be used to force the system into the debugger.[7]
On modern Windows "Alt + Print screen" (which is the shortcut for SysRq on most modern keyboards [4]) copies an image of the current active window, instead of the entire screen as Print Screen alone would.[8]
Similar keysedit
IBM 3270-type console keyboards of the IBM System/370mainframe computer, created in 1970, had an operator interrupt key that was used to cause the operating system such as VM/370 or MVS to allow the console to give input to the operating system.
system, request, system, request, sysrq, personal, computer, keyboards, that, standard, introduced, with, intended, available, special, directly, invoke, level, operating, system, functions, with, possibility, conflicting, with, existing, software, special, bi. System Request SysRq or Sys Req is a key on personal computer keyboards that has no standard use Introduced by IBM with the PC AT it was intended to be available as a special key to directly invoke low level operating system functions with no possibility of conflicting with any existing software A special BIOS routine software interrupt 0x15 subfunction 0x85 1 was added to signal the OS when SysRq was pushed or released Unlike most keys when it is pressed nothing is stored in the keyboard buffer A 104 key PC US English keyboard layout with System request circled Contents 1 History 2 Modern uses 3 Similar keys 4 See also 5 References 6 External linksHistory editThe 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 2 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 286 chip in the PC AT 3 unreliable source 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 task switching or 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 4 The default BIOS keyboard routines simply ignore SysRq and return without taking action So did the MS DOS input routines The keyboard routines in 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 debugging software the key is of no use for the vast majority of users On the Hyundai Hynix Super 16 computer pressing Ctrl SysRq will hard boot the system it will reboot when Ctrl Alt Del is unresponsive and it will invoke startup memory tests that are bypassed on soft boot citation needed Modern uses editIn Linux the kernel can be configured to provide functions for system debugging and crash recovery 5 This use is known as the magic SysRq key Microsoft has also used SysRq for various OS and application level debuggers In the CodeView debugger it was sometimes used to break into the debugging during program execution 6 For the Windows NT remote kernel debugger it can be used to force the system into the debugger 7 On modern Windows Alt Print screen which is the shortcut for SysRq on most modern keyboards 4 copies an image of the current active window instead of the entire screen as Print Screen alone would 8 Similar keys editIBM 3270 type console keyboards of the IBM System 370 mainframe computer created in 1970 had an operator interrupt key that was used to cause the operating system such as VM 370 or MVS to allow the console to give input to the operating system See also editSerial console Break key Scroll LockReferences edit Ralf Brown s Interrupt List Retrieved 2018 06 21 Original IBM PC Product fact sheet IBM Information Systems Division August 12 1981 Retrieved January 13 2010 Personal interview with Sandy Meade creator of the SysRq key a b What Are the Sys Rq Scroll Lock and Pause Break Keys on My Keyboard Retrieved March 2 2020 Linux Magic System Request Key Hacks Linux kernel Retrieved 2018 06 21 Returning Control to CodeView Microsoft Knowledge Base Archived from the original on November 8 2008 Retrieved January 8 2008 How to enable a remote kernel debugger connection on a computer that is running Windows Server 2003 with Service Pack 1 Microsoft Knowledge Base Archived from the original on October 21 2012 Retrieved January 8 2008 Copy the window or screen contents Retrieved March 2 2020 External links edit nbsp Media related to System request at Wikimedia CommonsIBM PC keyboard Windows ANSI US layout vteEsc F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 PrtScn SysRq ScrollLock Pause Break nbsp Insert Home PgUp NumLock Delete End PgDn 7 8 9 4 5 6 1 2 3 Enter 0 Ins Del Retrieved from https en wikipedia org w index php title System request amp oldid 1135252355, wikipedia, wiki, book, books, library,
