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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 DOS, Windows 3.0 and earlier version of Windows or OS/2, the key combination reboots the computer. Starting with Windows 3.1, the command invokes a task manager or security related component that facilitates ending a Windows session.
The soft reboot function via keyboard was originally designed by David Bradley. Bradley, as the chief engineer of the IBM PC project and developer of the machine's ROM-BIOS, had originally used Ctrl+Alt+Esc, but found it was too easy to bump the left side of the keyboard and reboot the computer accidentally. According to his own account, 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.
The feature was originally conceived only as an Easter egg 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". The feature, however, was detailed in IBM's technical reference documentation to the original PC and thereby revealed to the general public.
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."
Bradley is also known for his good-natured jab at Gates 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").
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 in to 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.
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. The BIOS reacts by performing a soft reboot (also known as a warm reboot). Examples of such operating systems include DOS, Windows 3.0 in Standard Mode as well as earlier versions of Windows.
In Windows 9x and Windows 3.0 running in 386 Enhanced mode, 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 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:
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 on Mac OS platforms. However, in the 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."
|This section does not cite any references or sources. (June 2013)|
In Linux, this keystroke combination is recognized by the keyboard device driver in the kernel. In the absence of more specific instructions, which will usually only be during system initialization, the kernel directly initiates a soft reboot in response. More commonly, the kernel will send a signal to the init process, which will perform an administrator-configured task, such as running a script, or displaying an "end current session" box in KDE.
In many Linux distributions, init is configured to switch run levels and to perform a soft reboot in response to the signal. Thus it provides a mechanism for a person with physical access to the keyboard to perform system shut down (a task that requires superuser rights to initiate programmatically). However, Linux systems can be configured to ignore the keystroke combination. The setting is usually in the inittab(5) configuration file under the keyword "ca".
Linux also has a similar sequence of keystrokes for restarting the computer described at the article Magic SysRq key.
Under the X Window System (the graphics display and windowing framework upon which most Linux and BSD GUIs are based), Control-Alt-Backspace kills the X server—normally killing all programs using it (including the window manager)—but not the underlying operating system. When a display manager is used, it restarts the killed X server.
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|BIOS||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).|
|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) and flushing disk caches (since DOS 6, or with FreeKEYB loaded). Some 386 memory managers (e.g. QEMM) can intercept and turn this into a quick reboot. If more than one task is running under multitaskers like DR-DOS EMM386 /MULTI + TASKMGR, this will only kill the currently running foreground task.|
|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.|
|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.|
|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|
|⌘ Cmd+⌥ Option+Control+⏏ Media Eject||Quit all applications and shut down|
|Control+⏏ Media Eject||Show restart, sleep or shutdown dialog|
|BeOS||Ctrl+Alt+⇧ Shift and click an applications entry in the Deskbar||Kills application|
|Xfce||Ctrl+Alt+Esc + click on window||Kills application|
|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.|
|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.|
|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)|
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"
LocalRebootbetween Windows 3.x and Windows 95
LocalRebootin Windows 95
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