Control-Alt-Delete

Control-Alt-Delete (often abbreviated to Ctrl+Alt+Del, also known as the "three-finger salute" or "Security Keys")[1][2] is a computer keyboard command on IBM PC compatible computers, invoked by pressing the Delete key while holding the Control and Alt keys: Ctrl+Alt+Delete. The function of the key combination differs depending on the context but it generally interrupts or facilitates interrupting a function. For instance, in pre-boot environment (before an operating system starts)[3][4][5] or in DOS, Windows 3.0 and earlier versions of Windows or OS/2, the key combination reboots the computer. Starting with Windows 95, the key combination invokes a task manager or security related component that facilitates ending a Windows session or killing a frozen application.

This article is about the keyboard combination. For other uses, see Control-Alt-Delete (disambiguation).

A QWERTY keyboard layout with the position of Control, Alt and Delete keys highlighted

History
Original IBM PC 5150 keyboard: It is impossible to press Ctrl+Alt+Del with one hand only

The soft reboot function via keyboard was originally designed by David Bradley.[6][7] Bradley, as the chief engineer of the IBM PC project and developer of the machine's ROM-BIOS, had originally used Ctrl+Alt+Esc,[8] but found it was too easy to bump the left side of the keyboard and reboot the computer accidentally. According to his own account, Mel Hallerman, who was the chief programmer of the project, therefore suggested switching the key combination to Ctrl+Alt+Del as a safety measure, a combination impossible to press with just one hand on the original IBM PC keyboard.[9][10][11]

The feature was originally conceived only as a development feature for internal use and not intended to be used by end users, as it triggered the reboot without warning or further confirmation—it was meant to be used by people writing programs or documentation so that they could reboot their computers without powering them down. Bill Gates (former Microsoft CEO) remembered it as "just something we were using in development and it wouldn't be available elsewhere".[12] The feature, however, was detailed in IBM's technical reference documentation[3] to the original PC and thereby revealed to the general public.[9]

Bradley viewed this work as just one small task out of many: "It was five minutes, 10 minutes of activity, and then I moved on to the next of the 100 things that needed to get done."[7] In a March 2018 email, one of Bradley's co-workers confirmed the command was invented in 1981 in Boca Raton, Florida.[13]

Bradley is also known for his good-natured jab at Gates at the celebration of the 20th anniversary of the IBM PC on August 8, 2001 at The Tech Museum: "I have to share the credit. I may have invented it, but I think Bill made it famous."; he quickly added it was a reference to Windows NT logon procedures ("Press Ctrl + Alt + Delete to log on").[14][10]

During a question and answer presentation on 21 September 2013, Gates said "it was a mistake", referring to the decision to use Ctrl+Alt+Del as the keyboard combination to log into Windows. Gates stated he would have preferred a single button to trigger the same actions, but could not get IBM to add the extra button into the keyboard layout.[8]

BIOS

By default, when the operating system is running in real mode (or in a pre-boot environment, when no operating system is started yet), this keystroke combination is intercepted by the BIOS.[3][4][5][15][16] The BIOS reacts by performing a soft reboot (also known as a warm reboot).[3][4][5][16] Examples of such operating systems include DOS, Windows 3.0 in Standard Mode as well as earlier versions of Windows.[8]

Windows

DOS-based Windows
Close Program dialog box, seen in Windows 9x

In Windows 9x and Windows 3.0 running in 386 Enhanced mode,[8] the keystroke combination is recognized by the Windows keyboard device driver. According to the value of the LocalReboot option in the [386Enh] section of system.ini, Windows performs one of several actions in response. If LocalReboot=On (default):

  • Windows 3.1x displays a blue screen that allows the user to press Enter to end a task that has stopped responding to the system (if such a task exists) or press Control+Alt+Delete again to perform a soft reboot.[17] The text of this rudimentary task manager was written by Steve Ballmer.[18]
  • Windows 9x temporarily halts the entire system and displays the Close Program dialog box, a window which lists currently running processes and allows the user to end them (by force, if necessary). The user can press Control+Alt+Delete again to perform a soft reboot.[19][20]

If LocalReboot=Off, Windows performs a soft reboot.[17][20]

Windows NT family
The Windows Security screen in Windows 8 provides various security-related options.
Windows 8 secure attention screen

The Windows NT family of operating system, whose members do not have "NT" in their names since Windows 2000, reserve Ctrl+Alt+Delete for the operating system itself. Winlogon, a core component of the operating system,[21] responds to the key combination in the following scenarios:

Invoking Windows Security
When a user is logged onto a Windows computer, pressing Ctrl+Alt+Delete invokes Windows Security. It is a graphical user interface that allows user to lock the system,[lower-alpha 1] switch user, log off, change the password, invoke Windows Task Manager, or end the Windows session by shutting down, rebooting or putting the computer into sleep or hibernation; clicking "Cancel" or pressing the Escape key returns the user to where they were.

The key combination always invokes Windows Security in all versions and editions of Windows NT family except Windows XP. (See below.) Prior to Windows Vista, Windows Security was a dialog box, did not allow user switching and showed the logon date and time, name of user account into which the user has logged on and the computer name. Starting with Windows Vista, Windows Security became full-screen.

Secure attention
Login spoofing is a social engineering trick in which a malicious computer program, masquerading as Windows login dialog box, prompts for user's account name and password to steal them. To thwart this attack, Windows NT implements an optional security measure in which Ctrl+Alt+Delete acts as a secure attention key combination. Once the protection is activated, Windows requires the user to press Ctrl+Alt+Delete each time before logging on or unlocking the computer. Since the key combination is intercepted by Windows itself and malicious software cannot mimic this behavior,[lower-alpha 2] the trick is thwarted.[22] Unless the Windows computer is part of a Windows domain network, the secure attention protection is disabled by default and must be enabled by the user.[23][24]
Windows XP behavior
Windows XP introduces Welcome Screen, a redesigned logon interface. The Welcome Screen of Windows XP, however, does not support the secure attention scenario.[24] It may be disabled in favor of the classic plain logon screen, either explicitly by the user or as a consequence of the Windows XP computer becoming part of a Windows domain network.[25] With that in mind, Windows XP uses the Ctrl+Alt+Delete in the following unique scenarios:
  1. At a logon prompt, the key combination dismisses Welcome Screen and invokes classic logon user interface.[25]
  2. When a user is logged on to a Windows XP computer and Welcome Screen is enabled, pressing the key combination invokes Windows Task Manager instead of Windows Security.[26]
Windows Vista and the next versions of Windows NT did not inherit any of the above.

OS/2

In OS/2, this keystroke combination is recognized by the OS/2 keyboard device driver, which notifies the session manager process.[27] The normal session manager process in OS/2 versions 2.0 and later is the parent Workplace Shell process, which displays the "system is rebooting" window and triggers a soft reboot.[28] If it is pressed twice in succession OS/2 triggers an immediate soft reboot, without waiting for the session manager process.

In both cases, the system flushes the page cache, cleanly unmounts all disc volumes, but does not cleanly shut down any running programs (and thus does not save any unsaved documents, or the current arrangements of the objects on the Workplace Shell desktop or in any of its open folders).[28][29]

Mac

Ctrl+Alt+Delete is not a keyboard shortcut on macOS. Instead, ⌘ Command+⌥ Option+Esc brings up the Force Quit panel. Control+⌘ Command+Power restarts the computer.[30]

The original Mac OS X Server had an Easter egg in which pressing Control+⌥ Option+Delete (as the Option key is the equivalent of Alt key on a Mac keyboard) would show an alert saying "This is not DOS!".[31]

Linux
The result of pressing the key combination in Ubuntu v12.10

On some Linux-based operating systems including Ubuntu and Debian, Control+Alt+Delete is a shortcut for logging out.[32]

On Ubuntu Server, it is used to reboot a computer without logging in.[33]

Equivalents on various platforms
Desktop operating systems
Platform Key combination Function
Amiga Ctrl+Left Amiga+Right Amiga Perform a hardware reboot by sending a reset signal to system via keyboard MCU (+ possible extra keycode + max 10s delay if "reset warning" is supported and in use).[34]
BIOS Ctrl+Alt+Delete Perform a soft reboot without memory initialization by jumping to IPL reset vector,[3][4][5][16] after broadcasting a pending shutdown event (on AT compatible machines).[4][5][35][16]
DOS + KEYB Ctrl+Alt+Delete Perform a soft reboot without memory initialization by jumping to IPL reset vector, after broadcasting a pending shutdown event (on AT compatible machines)[4][5][35] and flushing disk caches (since DOS 6, or with FreeKEYB[16][36][37] loaded). Some 386 memory managers (e.g. QEMM) can intercept and turn this into a quick reboot.[16] If more than one task is running under multitaskers like DR-DOS EMM386 /MULTI + TASKMGR, this will only kill the currently running foreground task.[16]
DOS + K3PLUS or FreeKEYB ⇧ Shift+Ctrl+Alt+Delete Perform a soft reboot with memory initialization (aka "cold reboot") by jumping to IPL reset vector, after broadcasting a pending shutdown event (on AT compatible machines) and flushing disk caches.[16][36][37][38]
LShift+RShift+Ctrl+Alt+Delete Perform a hard reboot by triggering the chipset's reset logic, after broadcasting a pending shutdown event and flushing disk caches.[16][36][37][38]
Windows 3.x Ctrl+Alt+Delete Close unresponsive applications. Performs a soft reboot if pressed twice.[17][19][20]
Windows 9x Ctrl+Alt+Delete Bring up "Close Program" dialog box (a simplistic task manager). Performs a soft reboot if pressed twice.[19][20]
Windows NT family Ctrl+⇧ Shift+Esc Bring up the Windows Task Manager[39]

Ctrl+Alt+Delete
Ctrl+Alt+End Used in Terminal Services to send the command to the remote session / application:
OS/2 Ctrl+Esc Bring up the Window List (unblocking the synchronous input queue)[42]
Ctrl+Alt+Delete Perform a soft reboot
Ctrl+Alt, NumLock (twice) Halt the system and begin a system dump to floppy disk
TOS (1.4 and higher), MiNT Ctrl+Alt+Delete Perform soft reboot without memory initialization (warm boot)[43]
RShift+Ctrl+Alt+Delete Perform soft reboot with memory initialization (cold boot)[43]
Linux Ctrl+Alt+Delete Signal the init process (usually configured to soft reboot)[44]
Alt+SysRq+function key Magic SysRq key: Depending on the function key, performs a certain low-level function. Examples: sync (flush caches), reboot (forced soft reboot), unmount (remount filesystems readonly), etc.
macOS ⌥ Option+⌘ Command+Esc Force quit applications[30]
⌘ Cmd+⌃ Control+⏏ Media Eject Quit all applications and restart[30]
⌘ Cmd+⌥ Option+⌃ Control+⏏ Media Eject Quit all applications and shut down[30]
Control+⏏ Media Eject Show restart, sleep or shutdown dialog[30][45]
Control+⌘ Command+Power Immediately restarts computer.[30]
BeOS Ctrl+Alt+⇧ Shift and click an application's entry in the Deskbar Kills application[46]
Xfce Ctrl+Alt+Esc + click on window Kills application (invokes xkill)[47]
Ctrl+Alt+Delete Lock the screen and invoke the screensaver
X Window System Ctrl+Alt+← Backspace Immediately kills the X server (the key can be disabled). When using an X Display Manager, it will usually start the X server again.
Other platforms
Platform Key combination Function
TI-30XIIS On+Clear Restarts the calculator and clears RAM
TI-80, TI-81, TI-82, TI-83, TI-84 Mode, Alpha, S Shows ROM version number. [Enter] enters self test mode
TI-85, TI-86 2nd, Mode, Alpha, S Shows ROM version number. [Enter] enters self test mode
TI-89 2nd+←+→+On Restarts the calculator and clears RAM
Esc+On Force break without restarting RAM
F5, ◆+Clear, Alpha+S Enter self test mode
Natural display Casio calculators ⇧ Shift+7+On Restarts the calculator and clears RAM and EEPROM. Continue pressing Shift to advance through self-test mode.
TI-99/4A FCTN+= Resets machine back to startup screen.
Voyage 200 2nd+Hand+On Restarts the calculator and clears RAM
HP-48 On+C Restarts RPL, clearing the Stack and PICT, closing IO, and returning to the HOME directory (but not purging the memory)
On+A+F As above, but also purges the memory
Scientific Atlanta Explorer DHCT
Samsung cable boxes		 Volume Down+Volume Up+Info (on settop box; not remote) Reboots box
Foxtel Set-top-boxes Back+Select (on box; except UEC 720) Power cycles the machine.[48]
Standby+Foxtel (on box; UEC 720)
Back+Select+Reset (on box; iQ2)
C64 Run/Stop+Restore Warm starts the machine, does not work if CPU has crashed or NMI is blocked in hardware or rerouted.
Amazon Fire TV Select+Play/Pause (on remote) Reboots the device

Cultural adoption
Dutch protester carrying a sign that reads "Ctrl-Alt-Del the early retirement plan"

As computers became ubiquitous, so too, has the jargon. Control-Alt-Delete can also mean "dump," or "do away with".[49]

The keystrokes are well known and infamous for escaping from problems in pop culture. For example, in the Billy Talent song "Perfect World", part of the lyrics include the sequence and associate it with resetting their memory and escaping from a situation: "Control-Alt-Deleted. Reset my memory."[50]

See also

Notes
  1. When a Windows computer is locked, access to Windows is only allowed when valid credentials are supplied. Unlocking a computer is similar to a logon.
  2. The only way to wrest the control of Ctrl+Alt+Delete handling from Windows is to subvert its core components such as kernel or winlogon. However, a malicious program that has succeeded in breaching Windows integrity so deeply does not need to steal a password.

References
  1. Smith, Gina (2007-12-03). "Unsung innovators: David Bradley, inventor of the "three-finger salute"". Computerworld. Archived from the original on 2014-07-15. Retrieved 2009-04-12.
  2. "CTRL-ALT-DEL: The Three Finger Salute". Togaware. Archived from the original on 2017-09-10. Retrieved 2009-04-12.
  3. IBM Personal Computer Technical Reference (Revised ed.). IBM Corporation. March 1983.
  4. IBM Personal Computer AT Technical Reference. IBM Personal Computer Hardware Reference Library. 0, 1, 2 (Revised ed.). IBM Corporation. March 1986 [1984-03]. 1502494, 6139362, 6183310, 6183312, 6183355, 6280070, 6280099.
  5. Phoenix Technologies, Ltd. (1989) [1987]. System BIOS for IBM PC/XT/AT Computers and Compatibles — The Complete Guide to ROM-Based System Software. Phoenix Technical Reference Series (1st ed.). Addison Wesley Publishing Company, Inc. ISBN 0-201-51806-6.
  6. "Unsung innovators: David Bradley, inventor of the "three-finger salute". Computerworld. 2007-12-03.
  7. Hughes, Virginia (2013-07-12). "The History of CTRL + ALT + DELETE". mental floss. Archived from the original on 2017-09-10. Retrieved 2013-07-10.
  8. Bright, Peter (2013-09-27). "If Bill Gates really thinks ctrl-alt-del was a mistake, he should have fixed it himself". Ars Technica. Condé Nast. Archived from the original on 2017-09-10. Retrieved 2013-10-01.
  9. Williams, Gregg (January 1982). "A Closer Look at the IBM Personal Computer". BYTE. 7 (1). p. 36. Retrieved 2013-10-19.
  10. Needleman, Rafe (2011-08-15). "Happy 30th Birthday to the IBM PC". CNET. CBS Interactive. Archived from the original on 2017-09-10. Retrieved 2013-01-12.
  11. Aamidor, Abe. "Thank this guy for 'control-alt-delete'". Indianapolis Star. Archived from the original on 2017-09-10. Retrieved 2010-09-09.
  12. Gross, Doug (2013-09-26). "Bill Gates: Control-Alt-Delete a mistake". CNN. Archived from the original on 2013-09-26. Retrieved 2013-09-26.
  13. Jarvis, Craig (2018-03-05). "Oops. NC needs to delete ctrl+alt+delete from list of state's inventions". News & Observer. Retrieved 2018-04-03.
  14. Control-Alt-Delete: David Bradley & Bill Gates, video clip from IBM PC 20th Anniversary, Aug 8, 2001 (posted to YouTube on Jan 7, 2011)
  15. Hyde, Randall (1996-09-30). "The Art of Assembly Language Programming". Archived from the original on 2012-12-12. Retrieved 2012-04-25.
  16. Paul, Matthias R. (2002-04-03). "[fd-dev] Ctrl+Alt+Del". freedos-dev. Archived from the original on 2017-09-09. Retrieved 2017-09-10.
  17. "Windows 3.1 Resource Kit SYSTEM.INI 386ENH Section A–L". Microsoft's KnowledgeBase article 83435 (1.0 ed.). 2001-07-30 [1992]. Archived from the original on 2016-03-20. Retrieved 2005-01-07. From SYSINI.WRI in Microsoft Windows Resource Kit for Windows 3.1: LocalReboot=<on-or-off>; Default: On; Purpose: Specifies whether you can press CTRL+ALT+DEL to quit applications that cause an unrecoverable errors in 386 enhanced mode, without restarting Windows. If this setting is enabled, you can quit the applications. If this setting is disabled, pressing CTRL+ALT+DEL will restart your entire system (as it normally does.)
  18. Chen, Raymond (2014-09-02). "Who wrote the text for the Ctrl+Alt+Del dialog in Windows 3.1?". The Old New Thing. Microsoft. Archived from the original on 2017-09-10. Retrieved 2014-09-10.
  19. Chappell, Geoff (1998-05-06). "Is this possible?". Newsgroup: comp.os.ms-windows.programmer.vxd. Usenet: 6iouc1$dgh$2@reader1.reader.news.ozemail.net. Archived from the original on 2017-09-10. Retrieved 2017-09-10. — a report of differences in LocalReboot between Windows 3.x and Windows 95
  20. Terhune, Gary S. (2004-01-11). "Lost Ctrl-Alt-Del function on W98, 2nd". Newsgroup: microsoft.public.win98.gen_discussion. Usenet: uAIVMjC2DHA.2336@TK2MSFTNGP09.phx.gbl. Archived from the original on 2013-10-02. Retrieved 2013-10-02. — a report of the effect of LocalReboot in Windows 95
  21. Andrei Miroshnikov (2018). Windows Security Monitoring: Scenarios and Patterns. ISBN 978-1119390879. Winlogon is a system component
  22. Osterman, Larry (2005-01-24). "Why is Control-Alt-Delete the secure attention sequence (SAS)?". Larry Osterman's WebLog. MSDN Blogs. Archived from the original on 2017-09-10. Retrieved 2007-03-15.
  23. "Enable Press Ctrl+Alt+Del Secure Logon On Windows 7 or Vista". My Digital Life. 2010-01-28. Archived from the original on 2017-09-10. Retrieved 2013-01-19.
  24. "How to enable or disable the CTRL+ALT+DELETE sequence for logging on to Windows XP, to Windows Vista, and to Windows 7". Microsoft Support. Microsoft. 2010-12-10. Retrieved 2013-01-19.
  25. "How to change the logon window and the shutdown preferences in Windows XP". Microsoft Support. Microsoft. 2007-05-07. Retrieved 2013-01-19.
  26. "Using CTRL+ALT+DEL key combination to open Windows Security opens Task Manager". Microsoft Support. Microsoft. 2006-01-15. Retrieved 2013-01-19.
  27. Iacobucci, Ed (1988). Das OS/2-Buch [OS/2 Programmer's Guide] (in German) (1st ed.). Hamburg: Osborne / McGraw-Hill Book Company GmbH (published 1989). ISBN 3-89028-151-6.
  28. Albrecht, Robert M.; Plura, Michael (1993). Das große Buch zu OS/2 Version 2 (in German) (1st ed.). Düsseldorf: Data Becker. ISBN 3-89011-598-5.
  29. Moskowitz, David; Kerr, David (1995). OS/2 Warp Version 3 für Insider [OS/2 Warp Unleashed Deluxe Edition] (in German) (1st ed.). SAMS Publishing. ISBN 3-87791-815-8.
  30. "Mac keyboard shortcuts". Apple, Inc.
  31. "Mac OS X Server Easter Egg - This is not DOS". Retrieved 2011-10-07.
  32. "Useful keyboard shortcuts". Ubuntu Desktop Guide. Canonical. Retrieved 2014-10-30.
  33. "Console Security". Ubuntu Server Guide. Canonical. Retrieved 2015-06-02.
  34. Wilen, Toni. "Is Ctrl-Amiga-Amiga something special?". English Amiga Board. Retrieved 2018-09-19.
  35. Paul, Matthias R. (2004-03-13). "Rebooting from user-space" (FreeDOS technical note). Archived from the original on 2017-01-16. Retrieved 2017-01-15.
  36. Paul, Matthias R.; Frinke, Axel C. (1997-10-13) [first published 1991], FreeKEYB - Enhanced DOS keyboard and console driver (User Manual) (v6.5 ed.) (NB. FreeKEYB is a Unicode-based dynamically configurable successor of K3PLUS supporting most keyboard layouts, code pages, and country codes.)
  37. Paul, Matthias R.; Frinke, Axel C. (2006-01-16), FreeKEYB - Advanced international DOS keyboard and console driver (User Manual) (v7 preliminary (v6.58) ed.)
  38. Frinke, Axel C.; Paul, Matthias R. (1995-05-10) [first published 1991], K3PLUS v6 - Der ultimative Ersatz für den DOS-Standard-Tastaturtreiber KEYB GR (User Manual) (in German) (r49-v6.21 ed.) (NB. K3PLUS was an extended keyboard driver for DOS widely distributed in Germany at its time, with adaptations to a handful of other European languages available. K3PLUS.DOC is part of the K3P621P2.ZIP distribution package.)
  39. "Keyboard Shortcuts". Oracle Help Center.
  40. "List of the keyboard shortcuts that are available in Windows XP". Microsoft.com.
  41. "List of Windows Keyboard Shortcuts".
  42. "Full text of "IBM OS 2 Warp 4 Foundation Level Training Manual"".
  43. "FreeMiNT-Portal - mint.doc". 2000-04-27. Archived from the original on 2017-01-15. Retrieved 2017-01-09.
  44. "Ctrl+Alt+Delete".
  45. "Mac OS X 10.4 or earlier: Computer stops responding". Apple, Inc.
  46. "The Haiku/BeOS Tip Server: Kill and restart the Tracker".
  47. "XFCE4 Keyboard Shortcuts". Technology of a Knucklehead. 2014-08-02.
  48. FOXTEL Set-Top Unit Reboot
  49. Wordspy cites the earliest such use as Chris Miksanek's 18 December 1995 Computerworld column titled, "Ctrl-Alt-Delete those holiday trinkets".
  50. "Billy Talent – 'Perfect World' Lyrics". Archived from the original on 2016-03-03. Retrieved 2011-07-13.

Further reading
  • Linux manual pages for kill(2) and reboot(2).
IBM PC keyboard (Windows, ANSI US layout)
Esc F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 PrtScn/
SysRq		 Scroll
Lock		 Pause/
Break
Insert Home PgUp Num
Lock		 ∕ ∗ −
Delete End PgDn 7 8 9 +
4 5 6
↑ 1 2 3 Enter
← ↓ →    0
   Ins		  . 
Del
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