Answer: Slowed the Processor
For hundreds of thousands of young computer users, the “Turbo” button was like a mystical power booster that could solve most computer ailments. Except that, counter-intuitively, the Turbo button was never designed to speed anything up, but to instead slow a computer down.
In the early days of computing, programmers relied heavily on the processor speed for timing. As a result, thousands of applications, such as early PC games, relied on the processor’s speed to govern the timing of in-application events. If you played a game that was intended to be played on a 33MHz system on a 66MHz system, for example, the game would run twice as fast and be rendered unplayable. The Turbo button served as a hardwired compatibility tool, and flipping the Turbo would slow down the processor and ensure that older software would run properly.
While the application of the button and the accompanying light wasn’t consistent across early computer manufacturers (some companies designed it so that pushing the button in would turn the light on and actually run the computer at full speed while others had it set so that clicking the button out and “off” would turn the turbo on), the button existed solely to allow the end user to dial back their computer’s processing power as needed. After all, if it wasn’t necessary to slow the processor down for some purposes, no company on earth would include a button that made the machine run below the advertised specifications.
On modern computers, this process is handled by the operating system or emulation software, and the Turbo button has gone the way of the 5.25″ floppy drive.