On IBM PC compatible computers, the turbo button selects one of two run states: the default "turbo" speed or a reduced speed closer to the Intel 8086 CPU. It was relatively common on computers using the Intel 80286, Intel 80386 and Intel 80486 processors, from the mid 1980s to mid 1990s. The name is inspired by turbocharger, a device which increases an engine's power and efficiency. When pressed, the "turbo" button is intended to let a computer run at the highest speed for which it had been designed. Purpose With the introduction of CPUs which ran faster than the original 4.77 MHz Intel 8088 used in the IBM Personal Computer, programs which relied on the CPU's frequency for timing were executing faster than intended. Games in particular were often rendered unplayable. To provide some compatibility, the "turbo" button was added. Disengaging turbo mode slows the system down to a state compatible with original 8086/8088 chips. Switching On most systems, turbo mode was with the button pushed in, but since the button could often be wired either way, on some systems it was the opposite.The turbo button could be linked to a turbo LED or two-digit segmented display on the system case, although in some cases, the indicated frequency (in MHz) was not a measure of the actual processor clocks, but the two "fast" and "slow" display options set by jumpers on the motherboard. Some systems also supported keyboard combinations -- and -- for switching turbo mode on and off, such as the Packard Bell 486ES 3x3 (the 4x4 and MT models had a dedicated Turbo button). With all the 486ES models—those with and without a turbo button—the power light would show green in normal (“Turbo”) mode, and orange in Slow mode. ITT Xtra used -- to toggle. Some keyboards had a turbo button as well, located near right Shift. Unlike the turbo button that was common on computer cases, the turbo button on the keyboards did not control the clock rate of the CPU; rather, it controlled the keyboard repeat rate. Turbo display The turbo display is used to display the current frequency (MHz) speed of the CPU, this is usually done by a two or three-digit digital LED display. The displayed speed can vary depending on the CPU's frequency, and the settings of the computer, however, it is not measuring the frequency of the CPU, it displays preset numbers