Turbo button
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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,[1] Intel 80386 and Intel 80486 processors,[2] 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.[3]
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 Ctrl-Alt-+ and Ctrl-Alt-- 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.[4] ITT Xtra used Ctrl-Alt-? to toggle.[citation needed]
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.[5]
Use
The feature was relatively common on systems running 286 to 486 CPUs,[6] and rarely on first generation Pentium CPU equipped computers.[citation needed] The frequency displays largely disappeared or were reprogrammed to display "HI"/"LO" when CPU speeds reached 100 MHz, since most systems only had a two-digit display.
As new computers continued to get faster and had a wide variety of available speeds, it became impossible for software to rely on specific CPU speed. As software began to rely on other timing methods, the turbo feature became mostly irrelevant to new programs.[7][8]
Software implementations
While the implementation of an actual hardware turbo button has disappeared on modern machines, software developers have compensated with software replacements. One example is DOSBox, which offers an adjustable emulation rate. Modern PCs that support ACPI power management may provide software controls to switch ACPI performance states or other CPU throttling modes. This is used for power saving or to prevent CPU overheating rather than for compatibility, as modern applications use the real time clock for timing instead of the CPU clock.
- Turbo PC by Complete Business Systems, @1991 - 1994, Ira Kleiner
- ^ 20-MHz 286 PCs, PC Magazine, June 27, 1989
- ^ Turbo button, Computer Hope, 10-17-2017
- ^ "Intel486 SL Microprocessor SuperSet Datasheet" (PDF). datasheetarchive.com. 2021-01-19. Archived from the original (PDF) on 2022-10-21. Retrieved 2022-10-21.
- ^ Packard Bell 486ES Personal Computer User’s Manual, pp. 4-1 to 4-3
- ^ Case, Loyd (2006-05-09). "Keyboards For Less". PC Magazine. Ziff Davis. p. 87. Retrieved 2018-01-07.
When you press the Turbo button simultaneously with one of the first seven Function keys, you can increase or decrease the speed of repeated keys.
- ^ "Eliminate Accidentally Turning Off Turbo Mode on Turbo PCs". Pcguide.com. 2001-04-17. Archived from the original on 2001-04-17. Retrieved 2020-01-14.
- ^ "Turbo Button". Pcguide.com. 2001-04-17. Archived from the original on 2001-07-12. Retrieved 2017-03-04.
- ^ "Electrifying Software For Today's PC". Compute! (advertisement). June 1988. p. 23. Retrieved 10 November 2013. 1988 game advertising automatic compensation for CPU speed.