Origin of the Three-Finger Salute (CTRL-ALT-DEL)

PC keyboard highlighting positions of Control, Alt, and Delete keys.

The idea for the CTRL-ALT-DEL key combination originated in the IBM PC group, during development of the original IBM PC in 1981. David Bradley wanted a key combination that could be used internally by developers to quickly reboot the computer,without having to power it down and back up again. Although it was never meant to be used out in the field by end users, it was documented in the IBM Technical Reference and soon became common knowledge in publicly-available documentation for the IBM PC, and the many compatible DOS-based machines that followed. In fact, documentation for some applications instructed users to insert the application diskette and press CTRL-ALT-DEL to install or start the software.

Originally CTRL-ALT-ESC, in which all three keys appeared on the left side of the original IBM PC keyboard, the sequence was quickly changed to CTRL-ALT-DEL to make it virtually impossible to accidentally reboot the computer with just one hand. Many of today’s PC keyboards replicate the CTRL and ATL keys on the right side of the keyboard, so it’s much easier today to perform the sequence with one hand, so the reason for changing from ESC to DEL has become a bit of an anachronism.

DOS software applications didn’t use this sequence, because their developers knew that it was the “reboot the computer” sequence. BIOS developers soon adopted the sequence to provide users with a familiar way to reboot the computer during the boot sequence, even before any operating system had loaded. OS/2 adopted the sequence, which was handled by the keyboard driver.

In 1989, during early Windows NT 3.1 development (at the time, NT OS/2), Microsoft needed a “secure attention sequence” that wouldn’t and couldn’t be intercepted by any application. The only keyboard combination that wasn’t already being used by a shipping application was CTRL-ALT-DEL. Over time, this became the sequence used in NT and its successors (all Server versions, and all desktop versions from XP onward) to securely get the attention of the system to log in, log off, lock the system, shut down, restart, etc. For example, requiring CTRL-ALT-DEL to log in ensures that the password screen you see is the actual password screen and not some other, nefarious software that is trying to steal your password by appearing to be the password screen.

CTRL-ALT-DEL remains with us today. Now you know who to blame.

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