Cntrl alt del
Control-Alt-Delete is a computer keyboard command on IBM PC compatible systems. It is given by simultaneously pressing the Control, Alt, and Delete keys. This command is a hook to the BIOS of a PC running DOS; it causes the computer to hard reboot.
This keyboard combination was chosen so that a reboot would be hard to cause accidentally. The code for this type of bailing out was written by David Bradley (IBM programmer) who allegedly once said "I may have invented it, but Bill made it famous."
In Microsoft Windows, this keyboard command is intercepted and is used to perform the following tasks:
- to bring up the Task Manager to kill errant processes
- to bring up the Login dialog
- to bring up the "Windows Security" dialog, where the user can lock the computer, change password, shut down, and so on.
This intercept in Windows exists for historical reasons. When early versions of Windows were built on top of MS-DOS, it was necessary to prevent a reboot by intercepting this key combination and using it for the security features mentioned above. If this had not been done, a hard reboot could have been used to bypass these security features.
In Linux, the command may also be intercepted, and can be used to initiate a soft reboot in situations where a normal shutdown procedure is unavailable (for example, if a normal user does not have the root permission necessary to shut down the computer).
Colloquially, the combination is also known as the three finger salute, or more esoterically, a Vulcan nerve pinch.
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