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pressed in, hence the name turbo. This caused a lot of confusion and misunderstanding about the purpose and naming of the button in retro computer forums and communities. This issue can be solved by reconnecting the wires in the correct way on either the display, or on the motherboard of the computer. If the turbo LED is on, that always means the CPU is running at full speed, regardless of how the switch is wired.
157:, programs which relied on the CPU's frequency for timing were executing faster than intended. Games in particular were often rendered unplayable, due to the reduced time allowed to react to the faster game events. To restore compatibility, the "turbo" button was added. Disengaging turbo mode slows the system down to a state compatible with original
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it displays preset numbers when turbo is turned on or off, and these numbers can be changed with two (or three) banks of jumpers on the back of the display, each bank changing each digit, as their purpose is to connect LED's in the display to (or disconnect from) power. The layout of the banks can vary.
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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,
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Some computers have wired the turbo button in a way that if the button is pressed in, the computer is running in the slower speed. While the turbo button can be configured this way, this is not the intended way of using the button, as the computer is intended to run at full speed when the button is
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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
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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.
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era computers. The frequency displays largely disappeared or were reprogrammed to display "HI"/"LO", "99", or were replaced with a three-digit display when CPU speeds reached 100 MHz, since most systems only had a two-digit display.
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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
75:, 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.
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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
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While the implementation of an actual hardware turbo button has disappeared on modern machines, software developers have compensated with software replacements. One example is
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based computer. The turbo button is the small button below the segment display; the amber light above is a secondary indicator of the turbo button state.
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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.
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selects one of two run states: the default "turbo" speed or a reduced speed closer to the
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With the introduction of CPUs which ran faster than the original 4.77 MHz
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processors, from the mid 1980s to mid 1990s. The name is inspired by
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Packard Bell 486ES Personal
Computer User’s Manual, pp. 4-1 to 4-3
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Turbo PC by
Complete Business Systems, @1991 - 1994, Ira Kleiner
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rather than for compatibility, as modern applications use the
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Some keyboards had a turbo button as well, located near right
468:"Eliminate Accidentally Turning Off Turbo Mode on Turbo PCs"
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of the CPU; rather, it controlled the keyboard repeat rate.
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1988 game advertising automatic compensation for CPU speed.
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power management may provide software controls to switch
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The feature was relatively common on systems running
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CPU. It was relatively common on computers using the
189:Some systems also supported keyboard combinations
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553:"Gigabyte 486 Motherboard User Manual (page 32)"
373:"Intel486 SL Microprocessor SuperSet Datasheet"
643:"Vextrec GMB 386 Motherboard Manual (Page 30)"
570:"Elicegroup 386 Motherboard Manual (Page 52)"
626:"FOX-III 286 Motherboard Manual (Page 3-10)"
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35:display showing the CPU clock frequency, in
410:The PC turbo button mystery finally solved!
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117:. Unsourced material may be challenged and
137:Learn how and when to remove this message
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609:"Magitronic 286 User Manual (Page 24)"
532:(advertisement). June 1988. p. 23
526:"Electrifying Software For Today's PC"
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115:adding citations to reliable sources
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589:Why Did Old PCs Have Turbo Buttons?
23:Case buttons including turbo button
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503:. 2001-04-17. Archived from
474:. 2001-04-17. Archived from
382:. 2021-01-19. Archived from
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362:, Computer Hope, 10-17-2017
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309:for timing instead of the
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438:Case, Loyd (2006-05-09).
264:CPUs, and less common on
446:. Ziff Davis. p. 87
317:Inverted button behavior
297:modes. This is used for
277:Software implementations
666:Computing input devices
291:ACPI performance states
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155:IBM Personal Computer
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440:"Keyboards For Less"
380:datasheetarchive.com
111:improve this section
301:or to prevent CPU
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586:Basinger, Clint,
176:segmented display
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534:. Retrieved
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476:the original
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448:. Retrieved
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391:. Retrieved
384:the original
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360:Turbo button
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299:power saving
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153:used in the
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109:Please help
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73:turbocharger
53:turbo button
52:
46:
536:10 November
501:Pcguide.com
472:Pcguide.com
444:PC Magazine
407:VWestlife,
348:PC Magazine
303:overheating
226:to toggle.
184:motherboard
61:Intel 80286
41:Intel 80486
660:Categories
595:2023-03-30
511:2017-03-04
482:2020-01-14
450:2018-01-07
416:2023-03-31
393:2022-10-21
326:References
237:clock rate
151:Intel 8088
127:March 2023
57:Intel 8086
311:CPU clock
293:or other
169:Switching
98:does not
530:Compute!
39:, of an
266:Pentium
232:⇧ Shift
182:on the
180:jumpers
165:chips.
119:removed
104:sources
79:Purpose
283:DOSBox
646:(PDF)
629:(PDF)
612:(PDF)
573:(PDF)
556:(PDF)
387:(PDF)
376:(PDF)
69:80486
65:80386
538:2013
287:ACPI
216:Ctrl
203:Ctrl
201:and
191:Ctrl
163:8088
159:8086
102:any
100:cite
67:and
31:The
262:486
260:to
258:286
252:Use
220:Alt
207:Alt
195:Alt
113:by
47:On
37:MHz
33:LED
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
