What did the Turbo button in old computers do?

Discussion in 'PC Hardware, Software and Displays' started by Cyan, Jul 16, 2019.

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  1. Cyan

    Cyan orange
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    I remember old MS-DOS computers (in the 90s) at my school which had a Turbo button. Did it make the computer run faster and take the CPU to the limit? My first computer had Windows 95 as the operating system, and a Pentium 100MHz CPU plus 32MB of RAM.

    I don't ever remember seeing a PC featuring a turbo button after Windows 95 came out, if my memory serves me right
     
  2. hoom

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    It was a 15 or 25Mhz (?) clock boost.
    Nobody ever turned it off & there was no reason to do so -> later just made higher clocked SKUs.
     
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  3. Silent_Buddha

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    Basically the CPU had a default speed for compatibility with older programs that expected a certain clock rate and a higher clockspeed that you could activate with the "Turbo" button.

    Outside of businesses and corporations it wasn't terribly critical if you broke things in a program by enabling Turbo, so in the home environment it was rarely not enabled.

    The closest modern analogy to this are games that are hard coded to say...30 FPS (usually console titles that target a fixed console hardware arch.), and break if you attempt to run them at a higher FPS, usually when ported to PC.

    Many PS4 games are like this, hence PS4-P was designed in such a way as to provide virtually identical resources to games that would break if they were given more resources than they were designed for. I "think" there's a user option that would basically do a "Turbo button" like effect of unlocking additional resources on PS4-P, but could potentially break things in those games.

    Regards,
    SB
     
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  4. homerdog

    homerdog donator of the year
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  5. orangpelupa

    orangpelupa Elite Bug Hunter
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    yeah turbo button was a "misname".

    Turbo ON = normal speed
    turbo off = slow mode
     
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  6. SlmDnk

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    As Buddha mentioned, some games and programs didn't work properly unless turbo was disabled. I remember having a couple of cases like that.
     
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  7. hoom

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    OK.
    Nobody I knew ever needed to turn it off :neutral:
     
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  8. Rurouni

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    I remember on several games that when turbo is on everything went fast. I think my first PC which had a turbo button in it doubled the speed from 8mhz-ish to 16mhz-ish so a lot of games roughly ran twice the speed with the turbo on. For me it was a fun button.
     
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  9. Malo

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    Yep there were games on my original XT that only went proper speed at 4.75Mhz instead of 10Mhz.
     
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  10. Sonic

    Sonic Senior Member
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    The turbo button was used for compatibility with older games and programs that ran too quickly on newer CPU"s back in the MS-DOS days. It lowered the speed of the processor to slow things down and make them run at a relatively normal speed compared to blazing fast speeds. It's counterintuitive because one would think thibgs wkd run faster with turbo enabmed but it was used to male things run slower.

    Wheb having turbo enabled didn't help enough to slow things down then that's when we went into Bios settings and disabled cache tl get klder games and programs to run at a normal sleed.
     
  11. AlBran

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    Gotta type fast. :eek:
     
  12. Sonic

    Sonic Senior Member
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  13. AlBran

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    Need a turbo button? ;)
     
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  14. DmitryKo

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    Yes, desktop AT cases in the i80286/i80386 era came with the Turbo button and a Turbo LED - replaced by a two-digit segmented display in i80486 era mini-tower cases; you would "program" the segments with jumpers to display CPU clocks or the letters "HI"/"LO".

    The 8 segments were lettered A-G clockwise, and each segment could be set to one of the 3 modes - turbo only, slow only, and both - or left unconnected for always off. This would allow values like 20/40, 25/50, and 33/66 MHz typical for the Intel 486DX/DX2 series and
    clones. There were also variants with additional leading "1" which could display 50/100, 60/120 and 66/133 MHz used by Intel 486DX4, AMD Am5x86, and Cyrix Cx5x86 processors.

    The default mode (jumper open) was indeed turbo speed (at least on "no-name" i80486 motherboards with an UMC chipset).


    Anyway this feature didn't make much sense by 1990s - most i286-era games were using programmable interrupt timers, so they ran just fine on significantly faster i386/ i486 processors.

    I don't think turbo switch was ever implemented on Pentium/MMX (P5/P54) motherboards based on i430 chipset series, and in 1995 the ATX form factor appeared which did not specify a turbo switch either.
     
    #14 DmitryKo, Aug 9, 2019
    Last edited: Aug 13, 2019
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  15. Malo

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    Oh the joys of configuring the jumpers on the case LEDs to match the right speeds. What a waste of time.
     
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  16. corysama

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    Oooh! Oooh! I know this one!

    The Turbo button found lots of uses over the years, but the original purpose was actually a backwards-compatibility feature to allow people who upgrade from the original 4.77Mhz IBM PC to faster clock rates to still have the option to use their NTSC TVs as computer monitors.

    The original IBM PC could have run at 5Mhz, but 4.77 was chosen instead because, in an obscure way, it aligned with the NTSC refresh rate. This allowed the CGA graphics card to output NTSC while being designed to piggyback on the CPU clock instead of shelling out pennies for one of it's own. But, when faster CPUs came out, that trick no longer worked and the TV output feature would be lost. To reassure everyone that buying a newer PC would not mean a loss of features, a "downclock back to 4.77Mhz" button was added to restore the feature when needed. "slomo-button" is not good marketing, so it was named Turbo.

    It was far more useful than originally intended because many early games were written assuming a fixed 4.77Mhz clock. After all, that was the PC standard! Later PCs included it mostly because it was expected. And, the rest is folklore!
     
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