Microsoft Word had so many shortcuts it collided with the Mac’s emergency abort keys
Andy Hertzfeld’s account of Switcher follows application isolation, compatibility work and the hunt for four unused keys.
Four keys should have been enough to stay out of trouble. Andy Hertzfeld chose Shift-Command-Option-Period as the emergency abort command for Switcher, his early Macintosh application-switching utility. Microsoft called: Word already used that combination. Even the escape route had a scheduling conflict.
In Hertzfeld’s firsthand account, Microsoft’s Jeff Harbers asked him to change it. Hertzfeld invited a replacement suggestion. Harbers called back the next day and withdrew the request: Word would change instead. His explanation was that the team could not find a safe sequence. “Every key combination,” as Hertzfeld recounts it, had apparently already found employment.
The collision came late in a much larger compatibility problem. Switcher let multiple applications remain in memory so a user could move among them quickly. It took advantage of the room available on the 512K Macintosh, while handling application-specific state that the system had kept in low memory. Software built around the assumption that it owned the machine suddenly had neighbors. Naturally, some of them left things in the hallway.
Hertzfeld chose separate heap zones to help isolate applications. Context switching also required identifying and swapping global variables so each program found its expected state on return. The hard part was the precise list, including subtle dependencies in how applications used the system. Switching the screen looked quick because an awful lot of invisible housekeeping had to be correct first.
The source describes a scrolling transition between applications and a demonstration involving MacWrite, MacPaint, MacDraw and the Finder. That animation made the switch legible. It did not do the isolation work by itself. Modern interfaces can still confuse those two layers: a smooth visual transition is reassuring, but the underlying program state is what decides whether the next click survives.
Microsoft’s applications were especially painful to debug in Hertzfeld’s telling because their instructions used an interpreted pseudo-code representation. He describes single-stepping through the interpreter in groups of instructions to reach the work being done. A broad promise to support existing software becomes very specific when one application’s crash needs that much attention.
The abort feature aimed to stop one hung application from taking down all the others. Hertzfeld monitored for the unusual key combination from the vertical blanking interrupt handler. Choosing something hard to press accidentally protected the user from an emergency exit with a hair trigger. Learning that Word had claimed it turned the keyboard from a control surface into a fully leased office building.
The finished Switcher arrived in April 1985, according to the account. Hertzfeld later handed it off to Phil Goldman, who went on to work on MultiFinder with Erich Ringewald. The anecdote leaves a useful compatibility question for any new system-wide shortcut: which applications have already spent those keys? A shortcut inventory could answer that before a release, although a crowded application may still make the answer unpleasantly comprehensive.
Word had the last shortcut.