||This article needs additional citations for verification. (January 2011)|
Control-Alt-Delete (often abbreviated to Ctrl+Alt+Del, also known as the "three-finger salute") 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) or in MS-DOS, Windows 3.0 and earlier version of Windows, the key combination reboots the computer. Starting with Windows 3.1x, in Windows, the command invokes a task manager or security related component that facilitates ending a Windows session. In OS/2, it invokes session manager. In most X Window System desktops, it brings up the logout dialog box.
In popular culture, the phrase "Control-Alt-Delete" may be used metaphorically to mean "to do away with" something.
The iconic adoption of this keyboard combination came from David Bradley, a designer of the original IBM PC. Bradley originally designed Ctrl+Alt+Esc to trigger a soft reboot (without warning or confirmation by the user), but he found it was too easy to bump the left side of the keyboard and reboot the computer accidentally. He switched the key combination to Ctrl+Alt+Del, a combination that was impossible to press with just one hand on the original IBM PC keyboard.
Bradley is also known for his good-natured jab at Bill Gates (former Microsoft software developer and CEO) at the celebration of the 20th anniversary of IBM PC: "I may have invented it, but Bill made it famous"; he quickly added it was a reference to Windows NT logon procedures ("Press Ctrl + Alt + Delete to log on").
In pre-boot environment (when no operating system is started yet) or when the operating system is running in real mode, by default, this keystroke combination is intercepted by BIOS. BIOS reacts by performing a soft reboot (also known as a warm reboot). Example of such operating system includes DOS, Windows 3.0 and earlier, or Windows 3.1x in Standard Mode.
DOS-based Windows 
In Windows 3.1x running in 386 Enhanced mode, Windows 95, Windows 98 and Windows Me, 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.
- Windows 95, Windows 98 and Windows Me temporarily halt the entire system and displays 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.
If LocalReboot=Off, Windows performs a soft reboot.
Windows NT family 
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, 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,[a] switch user, log off, change password, invoke Windows Task Manager or end Windows session by shutting down, rebooting or putting the computer into sleep or hibernation. 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
- Logon 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,[b] the trick is thwarted. 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.
- 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. 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. With that in mind, Windows XP uses the three-finger salute in the following unique scenarios:
- At a logon prompt, the key combination dismisses Welcome Screen and invokes classic logon user interface.
- 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.
- Windows Vista and the next versions of Windows NT did not inherit any of the above.
In OS/2, this keystroke combination is recognized by the OS/2 keyboard device driver, which notifies the session manager process. The normal session manager process in OS/2 versions 2.0 and later is the parent Workplace Shell process, which displays the "The system is rebooting" window and triggers a soft reboot. 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).
Ctrl+Alt+Delete is not a keyboard shortcut for anything on Mac OS platforms. However, in Mac OS X Server logon screen, pressing Control+⌥ Option+Delete (as the Option key is the equivalent of Alt key on a Mac keyboard) will show an alert saying "This is not DOS." 
Equivalents on various platforms 
||This section needs additional citations for verification. (July 2011)|
|DOS||Ctrl+Alt+Delete||Perform a soft reboot|
|Windows 3.x||Ctrl+Alt+Delete||Close unresponsive applications. Performs a soft reboot if pressed twice.|
|Windows 9x||Ctrl+Alt+Delete||Bring up "Close Program" dialog box (a simplistic task manager). Performs a soft reboot if pressed twice.|
|Windows NT family||Ctrl+⇧ Shift+Esc||Bring up the Windows Task Manager|
|OS/2||Ctrl+Esc||Bring up the Window List (unblocking the synchronous input queue)|
|Ctrl+Alt+Delete||Perform a soft reboot|
|Ctrl+Alt, NumLock (twice)||Halt the system and begin a system dump to floppy disk|
|Linux||Ctrl+Alt+Delete||Signal the init process (usually configured to soft reboot)|
|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...|
|Mac OS (7 and later)||⌥ Option+⌘ Command+Esc||Force quit applications|
|⌘ Cmd-Control–⏏ Media Eject||Quit all applications and restart|
|Control-⏏ Media Eject||Restart, sleep or shutdown|
|BeOS||Ctrl+Alt+⇧ Shift and click an applications entry in the Deskbar||Kills application|
|Xfce||Ctrl+Alt+Esc + click on window||Kill application|
|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 operating systems||Ctrl+Alt+Delete||Often (but not always) configured to reboot|
|Acorn Machines (pre-1987)||Break||Processor reset, although confusingly always referred to as soft reset. Hold down Ctrl as well for so-called hard reset (reinitializes various settings); hold down Shift to boot from disk (or not to, if disk is the default).|
|Acorn and post-Acorn RISC OS machines.||Reset button||Processor reset, although confusingly always referred to as soft reset. Hold down Ctrl as well for so-called hard reset (reinitializes various settings); hold down Shift to boot from disk (or not to, if disk is the default). Hold down various other keys to restore CMOS settings to safe configurations.|
|Ctrl+Break||Perform a soft reboot.|
|Amiga||Ctrl+Left Amiga (or Commodore)+Right Amiga||Hard reset. The reset will be instant unless a specific hardware delay function has been activated.|
|Amstrad CPC 464 and CPC6128||Ctrl+⇧ Shift+Esc||Reset (cold)|
|Amstrad PCW||⇧ Shift+Extra+Exit||Reset (cold)|
|⇧ Shift+Extra+Relay||Warm boot from the currently-inserted floppy disc. Is able to boot from discs in LocoScript installer format, which cannot be loaded by the normal ROM loader.|
|Atari ST||Ctrl+Alt+Del||Soft reset. Under FreeMiNT >= 1.16 it won't be instant, disk partitions are unmounted first. Ctrl + Alt + Shift + Del will perform hard reset.|
|Sinclair ZX Spectrum||Break||Halted peripheral (cassette tape or printer) operations with the report D BREAK – CONT repeats, or halted BASIC programs with the report L BREAK into program.|
|Alphas running OpenVMS||Ctrl+P||Enter ROM Serial Console or reboot, depending on setting in SRM|
|Apple II series machines||Ctrl+Reset||Enter the monitor or ROM BASIC|
|Ctrl+Open Apple+Reset||Reboot the machine|
|Ctrl+Option (Closed Apple)+Reset||Enter BIOS setup, then reboot|
|Ctrl+Option (Closed Apple)+Open Apple+Reset||Self-test, then reboot|
|Ctrl+Open Apple+Escape||Kill application|
|Macintosh computers with power button on keyboard||Control+⌘ Command+Power (sometimes known as a "Control Flower Power")||Reboot the machine|
|SGI workstation||Left Shift+Left Ctrl+Left Alt+Keypad Divide+F12||Restart X server (same as Ctrl + Alt + Backspace below). Nicknamed "the death-grip" due to the contorted finger positions.|
|Commodore 64 & Vic-20||Run/Stop+Restore||Halt (soft reconfiguration) and return to READY prompt|
|Commodore 128||Reset||Reset to power on state in current mode|
|Commodore+Reset||Reset to C-64 mode|
|Run/Stop+Reset||Reset to ML monitor preserving contents of BASIC memory|
|Olivetti M20||Ctrl+Reset||Soft resets the machine|
|TI Explorer Lisp Machine||Left-Ctrl Left-Meta Right-Ctrl Right-Meta Abort||Restart the system|
|BlackBerry||Alt+Right shift+Delete||Soft reboot|
|S60 Platform||Green (call answer)+*+3 (while restarting the phone)||Wipes internal memory and resets the device|
|iPod nano 3rd Generation||Play/Pause+Center button (hold down until Apple logo shows)||Reboots the iPod to the Apple logo that you see when you turn the iPod on for the first time.|
|iPod nano 4th Generation||≣ Menu+Center button (hold down until Apple logo shows)||Reboots the iPod to the Apple logo that you see when you turn the iPod on for the first time.|
|iPod Touch, iPhone, and iPad||Top Power Button+Center Home Button (hold down until Apple logo shows)||Reboots the iPod, iPhone, or iPad to the Apple logo that you see when you turn the device on for the first time.|
|Android devices, particularly the Nexus One||Track ball+volume down+power, all held down until power off||Reboot normally if all buttons are released; reboot into bootloader if the volume down button is continuously held|
|Alt+⇧ Shift+Del||Reboots the device. Applies to devices with a keyboard, such as Motorola Droid and Motorola Droid 2|
|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+Left Arrow+Right Arrow+On||Restarts the calculator and clears RAM|
|Esc+On||Force break without restarting RAM|
|F5, Diamond+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||Volume Down+Volume Up+Info (on settop box; not remote)||Reboots box (starts up to blue EXPLORER screen)|
|Foxtel Set-top-boxes||Back+Select (on box; except UEC 720)||Power cycles the machine.|
|Standby+Foxtel (on box; UEC 720)|
|Back+Select+Reset (on box; iQ2)|
In popular culture 
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."
They were also used in a line in the "Weird Al" Yankovic Song - It's all about the Pentiums:
"Play me online? Well, you know that I'll beat you.
If I ever meet you I'll Control-Alt-Delete you"
On the CBS hit sitcom "Two and a Half Men" the three couch throw pillows each have the letters CTRL, ALT and DEL printed on them in order.
See also 
- 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.
- 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.
- Smith, Gina (3 December 2007). "Unsung innovators: David Bradley, inventor of the "three-finger salute"". Computerworld. Retrieved 12 April 2009.
- "CTRL-ALT-DEL: The Three Finger Salute". Togaware. Retrieved 12 April 2009.
- "Slang Dictionary". Reference.com. Retrieved 8 July 2012. Text " Dictionary.com " ignored (help)
- Needleman, Rafe (15 August 2011). "Happy 30th Birthday to the IBM PC". CNET. CBS Interactive. Retrieved 12 January 2013.
- "Thank this guy for ‘control-alt-delete’". Indianapolis Star. Retrieved 2010-09-09.
- Needleman, Rafe (12 August 2011). "Ep. 87: Happy 30th birthday, IBM PC!". CNET. CBS Interactive. Retrieved 12 January 2013.
- Hyde, Randall (30 September 1996). "The Art of Assembly Language Programming". Retrieved 25 April 2012.
- "Microsoft Releases Windows 3.1". 6 April 1992. Retrieved 25 April 2012.
- Osterman, Larry (24 January 2005). "Why is Control-Alt-Delete the secure attention sequence (SAS)?". Larry Osterman's WebLog. MSDN Blogs. Retrieved 15 March 2007.
- "Enable Press Ctrl+Alt+Del Secure Logon On Windows 7 or Vista". My Digital Life. 28 January 2010. Retrieved 19 January 2013.
- "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. 10 December 2010. Retrieved 19 January 2013.
- "How to change the logon window and the shutdown preferences in Windows XP". Microsoft Support. Microsoft. 7 May 2007. Retrieved 19 January 2013.
- "Using CTRL+ALT+DEL key combination to open Windows Security opens Task Manager". Microsoft Support. Microsoft. 15 January 2006. Retrieved 19 January 2013.
- "Mac OS X Server Easter Egg - This is not DOS". Retrieved 7 October 2011.
- "Mac OS X keyboard shortcuts". Apple, Inc.
- "Mac OS X 10.4 or earlier: Computer stops responding". Apple, Inc.
- "Frozen or unresponsive iPhone".
- FOXTEL Set-Top Unit Reboot
- Wordspy cites the earliest such use as Chris Miksanek's 18 December 1995 Computerworld column titled, "Ctrl-Alt-Delete those holiday trinkets".
- "Billy Talent – 'Perfect World' Lyrics". Retrieved 13 July 2011.
- "Weird Al" Yankovic – 'it's all about the pentiums' Lyrics". Retrieved 26 October 2011.
Further reading 
- "Windows 3.1 Resource Kit SYSTEM.INI 386ENH Section A–L". Microsoft's KnowledgeBase article 83435. Retrieved January 7, 2005.
- Linux manual pages for kill(2) and reboot(2).
- Gary S. Terhune (11 January 2004). "Lost Ctrl-Alt-Del function on W98, 2nd". microsoft.public.win98.gen_discussion. — a report of the effect of
LocalRebootin Windows 95
- Geoff Chappell (6 May 1998). "Is this possible?". comp.os.ms-windows.programmer.vxd. (Web link). — a report of differences in
LocalRebootbetween Windows 3.x and Windows 95