IBM engineer David Bradley wrote the Ctrl+Alt+Del key combination into the original IBM PC in 1981 so the machine could be restarted without being switched off. He meant it for programmers and people writing computer documentation, and did not intend it for customers, according to a profile by the Lemelson-MIT Program.

Bradley was one of the 12 engineers on the team that built the PC, and he wrote its ROM BIOS.

A powered-down machine needed a few seconds to rest before powering up again to avoid damaging the hardware. Bradley’s team was looking for a simple way to reboot the PC without shutting it off, should it freeze or fail unexpectedly.

Why three keys

Bradley told Computerworld in 2007 that the new design “was hanging all the time”. The only fix was to turn the computer off and on, which took at least a minute because of the Power On Self Test. Rebooting “could be daily, hourly, even every five minutes if you were working on a particular shortcut,” he said.

He chose three keys that were hard to press together by accident.

The computer’s inner workings required two shift keys, and the Delete key sat at the other end of the keyboard. Pressing all three gave the same result as switching the machine off and on, without running POST.

Bradley has said the idea took him a few minutes and that he expected it to be used only internally or by engineers. It got out anyway. Computerworld reports that application developers, in the days when programs ran on diskette, published the combination to help users start their applications faster.

Microsoft later adopted it for Windows for use when software fails. Mental Floss says the fix spread from friend to friend in the early 1990s as Windows took off and PCs crashed.

The 2001 panel

In August 2001 Bradley sat on a panel with Bill Gates and other industry figures to mark the 20th anniversary of the IBM PC. Mental Floss reports that hundreds of people packed the San Jose Tech Museum of Innovation for the event, and that the first question after dinner went to Bradley instead of Gates.

“I have to share the credit,” he said. “I may have invented it, but I think Bill made it famous.”

That wording comes from reports of the event, including GeekWire, which posted a video of the panel in 2013, and Mental Floss. Computerworld later quoted Bradley recalling the line slightly differently: “I may have invented it, but Bill [Gates] is the one who made it famous.” He received a glare from Gates in return, Computerworld says.

Bradley later said Gates took the joke “very nicely” and sent a letter when he retired, GeekWire reported.

Gates told a Harvard University audience in 2013 that Microsoft’s use of Ctrl+Alt+Del to start Windows log-ons was “a mistake”, GeekWire reported. He said the company would have preferred a single key, but the IBM keyboard designer at the time did not want to give them one.

Bradley told Computerworld the combination was a final Jeopardy question in November 2002, when host Alex Trebek read: “IBM engineer Dave Bradley is called the father of this multikey combination.” Bradley retired from IBM in January 2004 after a 28-year career.

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