A friend of mine recently asked what the purpose of the old “Turbo button” was on old computers. Many today won’t remember a time when PCs were a fairly new concept and there used to be a button on some systems that changed the speed of the system.

Now, the question arose for obvious reasons: why would you ever want your computer to not be turbo? Isn’t the big push always for more speed in computers?

The answer requires us to go back to the beginning. The original compatible PCs had such speeds as 25 MHz (my first Windows 3.1 PC). Video game programmers used to make shortcuts in their programming, relying on the limitations of the CPU to set speed boundaries. In games such as Wolfenstein, one would hit the “walk forward” button, and the animations and movement speed were limited by the CPU processing power.

The problem came when processors started speeding up. It was not long before 100 or 133 MHz CPUs became available, and suddenly hitting the forward button would turn the game into an approximation of “the Flash” and you would launch at impossible speeds into death because the game was scaling faster with the processor. 4x faster CPU translated into things happening 4x faster (or more) in the game.

The Turbo button was a solution that allowed computers to scale back their speed to enable compatibility for these older games.

It may seem counterintuitive to have a button labeled “Turbo” whose purpose is to hobble a processor’s ability, but when you consider that when the button is pressed, the system is at full speed and when inactive the CPU is in the limitation mode, it makes more sense.

Today, systems have software solutions to such problems to virtualize ancient software environments to play such games. One such example is DOSBOX. Lucasarts’ SCUMMVM is another example of legacy gaming software virtualization.