What Sticky Keys Actually Does: Visual Breakdown of Every Modifier State

An insightful review of What Sticky Keys Actually Does: Visual Breakdown of Every Modifier State—read on to discover the main takeaways.

To understand what Sticky Keys does under the hood, you have to look at how computer keyboards interpret commands. Human-computer interface pioneer Jef Raskin famously coined the term "quasimode" to describe an interface state maintained only as long as the user physically presses and holds a button. On standard keyboards, modifier keys, Shift, Control, Alt, and the Windows or Command key, are classic quasimodes. To capitalize a letter, you hold Shift while striking the letter key. To copy text, you hold Control while tapping C.

This design presupposes that the user has two functional hands, ten flexible fingers, and adequate motor control to sustain steady downward pressure on two distant keyboard locations at once. For users who type with one hand, a mouth stick, an eye-tracking head pointer, or a prosthetic limb, a quasimode represents an impenetrable barrier. Striking Ctrl + Alt + Delete simultaneously requires spanning nearly the entire width of a standard keyboard deck.

Sticky Keys dismantles this barrier by converting a quasimode into a true system mode. It tells the operating system's keyboard driver to hold the modifier down in software memory even after your finger leaves the physical switch. The operating system serializes the keystrokes. You tap Control. You release it. You tap Alt. You release it. You tap Delete. The operating system pools these serialized keystrokes into a single system interrupt and executes the command as if all three keys were depressed at the exact same millisecond.