Editing Turbo button

{{short description|Computer button}}
[[File:PC-Front Turbotaste IMGP5528 smial wp.jpg|thumb|right|Case buttons including turbo button]]
[[File:486er 33MHz DX2 Double Speed Iomega Tape.jpg|thumb|The [[Light emitting diode|LED]] display showing the CPU clock frequency, in [[megahertz|MHz]], of an [[Intel 80486]] 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.]]

On [[IBM PC compatible|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]],<ref>[https://books.google.com/books?id=h6qtgYAzqDgC&pg=PA68 20-MHz 286 PCs], [[PC Magazine]], June 27, 1989</ref> [[i386|80386]] and [[i486|80486]] processors,<ref>[https://www.computerhope.com/jargon/t/turbo.htm Turbo button], Computer Hope, 10-17-2017</ref> 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.<ref>{{cite web |date=2021-01-19 |title=Intel486 SL Microprocessor SuperSet Datasheet |url=https://datasheet.datasheetarchive.com/originals/scans/Scans-101/DSAIHSC000148912.pdf |archive-url=https://web.archive.org/web/20221021042430/https://datasheet.datasheetarchive.com/originals/scans/Scans-101/DSAIHSC000148912.pdf |archive-date=2022-10-21 |archive-format=PDF |access-date=2022-10-21 |website=datasheetarchive.com}}</ref>

== Purpose ==

With the introduction of CPUs which ran faster than the original 4.77&nbsp;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, due to the reduced time allowed to react to the faster game events. To restore compatibility, the "turbo" button was added.<ref>{{Citation |last=VWestlife |title=The PC turbo button mystery finally solved! |date= 14 February 2023|url=https://www.youtube.com/watch?v=zpq9irl2yE4 |access-date=2023-03-31}}</ref> Disengaging turbo mode slows the system down to a state compatible with original [[Intel 8086|8086]]/[[Intel 8088|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 [[Jumper (computing)|jumpers]] on the [[motherboard]].

Some systems also supported keyboard combinations {{keypress|Ctrl}}-{{keypress|Alt}}-{{keypress|+}} and {{keypress|Ctrl}}-{{keypress|Alt}}-{{keypress|-}} 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.<ref>Packard Bell 486ES Personal Computer User’s Manual, pp. 4-1 to 4-3</ref> ITT Xtra used {{keypress|Ctrl}}-{{keypress|Alt}}-{{keypress|?}} to toggle.{{citation needed|date=November 2014}}

Some keyboards had a turbo button as well, located near right {{key top|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.<ref>{{cite magazine|last=Case|first=Loyd|date=2006-05-09|title=Keyboards For Less|url=https://books.google.com/books?id=WBftkMjnokEC&pg=PA87|magazine=PC Magazine|publisher=Ziff Davis|page=87|access-date=2018-01-07|quote=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.}}</ref>

== 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 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.

== Use ==

The feature was relatively common on systems running [[Intel 80286|286]] to [[Intel 80486|486]] CPUs,<ref name="pcguide2">{{cite web|url=http://www.pcguide.com/opt/opt/misc_Turbo.htm |title=Eliminate Accidentally Turning Off Turbo Mode on Turbo PCs |website=Pcguide.com |date=2001-04-17 |access-date=2020-01-14|archive-url=https://web.archive.org/web/20010417175150/http://www.pcguide.com/opt/opt/misc_Turbo.htm|archive-date=2001-04-17}}</ref>
and less common on [[Pentium]] 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&nbsp;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.<ref name="pcguide">{{cite web|url=http://www.pcguide.com/ref/case/switchTurbo-c.html |title=Turbo Button |website=Pcguide.com |date=2001-04-17 |access-date=2017-03-04| archive-url=https://web.archive.org/web/20010712011825/http://www.pcguide.com/ref/case/switchTurbo-c.html|archive-date=2001-07-12}}</ref><ref name="compute198806">{{cite news | url=https://archive.org/stream/1988-JUn-compute-magazine/Compute_Issue_097_1988_JUn#page/n23/mode/2up | title=Electrifying Software For Today's PC | work=Compute! | date=June 1988 | access-date=10 November 2013 | pages=23 | type=advertisement}} 1988 game advertising automatic compensation for CPU speed.</ref>

== 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 [[Advanced Configuration and Power Interface|ACPI]] power management may provide software controls to switch [[Performance state|ACPI performance states]] or other [[CPU throttling]] modes. This is used for [[power saving]] or to prevent CPU [[Overheating (electricity)|overheating]] rather than for compatibility, as modern applications use the [[real-time clock]] for timing instead of the [[CPU clock]].

== Inverted button behavior ==

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 pressed in, hence the name turbo.<ref>{{Cite web |title=Gigabyte 486 Motherboard User Manual (page 32) |url=https://www.minuszerodegrees.net/manuals/ECS/ECS-386_32%20System%20Board%20-%20Users%20Manual.pdf}}</ref><ref>{{Cite web |title=Elicegroup 386 Motherboard Manual (Page 52) |url=https://www.minuszerodegrees.net/manuals/ECS/ECS-386_32%20System%20Board%20-%20Users%20Manual.pdf}}</ref> This caused a lot of confusion and misunderstanding about the purpose and naming of the button in retro computer forums and communities{{fact|date=March 2023}}. 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.<ref>{{Citation |last=Basinger |first=Clint |title=Why Did Old PCs Have Turbo Buttons? |date=24 August 2015 |url=https://www.youtube.com/watch?v=p2q02Bxtqds |access-date=2023-03-30 |language=en}}</ref><ref>{{Cite web |title=Magitronic 286 User Manual (Page 24) |url=http://toastytech.com/manuals/Magitronic%20B233%20Manual.pdf}}</ref><ref>{{Cite web |title=FOX-III 286 Motherboard Manual (Page 3-10) |url=https://theretroweb.com/motherboard/manual/octek-fox-iii-286-12-16-20-mhz-versions-61b0798775c75130339205.pdf}}</ref><ref>{{Cite web |title=Vextrec GMB 386 Motherboard Manual (Page 30) |url=https://minuszerodegrees.net/manuals/Gemlight/GMB-486SG%20486%20VLB%20Motherboard%20-%20User's%20Manual%20-%20Edition%206.03.pdf}}</ref>

== References ==
{{commonscat}}
*Turbo PC by Complete Business Systems, @1991 - 1994, Ira Kleiner
{{Reflist}}

[[Category:Computing input devices]]
[[Category:Computer keys]]