Turbo Button Pays Charming Homage To Early Personal Computers

A personal computer drive bay with a glowing LED display

The PC turbo button and LED clock speed display were common features on early personal computers. Wanting to add a little retro chic to his modern battle-station, [Matthew Frost] assembled a charming and functional homage to the turbo button control panel.

In days past, this automotive nomenclature implied a performance boost when activated. Instead, ‘turbo mode’ would clock your x86 processor at its rated speed. Disabling ‘turbo’ would throttle the CPU, often all the way down to 4.77MHz. Inherited from the original IBM PC, some early computer programs relied on this specific clock speed, and would otherwise run too fast (or not at all) on faster hardware. PC marketing teams and engineers alike stopped including the turbo button and glowing clock speed numbers around the Pentium era.

This modern re-imagining of the turbo button uses an Arduino microcontroller, seven-segment display and tactile switches to emulate the look and feel of the original hardware. Instead of directly adjusting the CPU clock speed, hitting turbo switches between balanced and high-performance Windows power plans. The seven-segment display measures this clock speed in GHz to two decimal places. We’ll admit that it’s pretty satisfying to see those numbers inch higher when switching to turbo.

The rightmost button switches between measuring CPU speed, GPU utilization, network load and memory utilization, which improves on its original inspiration. The tubular key lock, also a common sight on early PCs, enables and disables networking for the entire system, which is great for keeping the kids off the ‘net (at least until they figure out how to remove the 5.25″ drive bay from the system and hot-wire the network adapter with a paperclip).

There are more details on the GitHub page, in case you want to build your own. This project could look especially fetching in PC sleeper builds, where new components are ‘hidden’ in old case hardware. And if this has made you feel nostalgic at all, you may want to hear our thoughts on why it’s all about the Pentiums.

33 thoughts on “Turbo Button Pays Charming Homage To Early Personal Computers

  1. When I got my first PC – a 286/12- in 1989, I often ran it at 8 MHz with the turbo button OFF because I was worried that running it on Turbo would burn it out! I was 13… had no idea. Also had no idea later that you could just change the jumpers to show any number you wanted. So when a guy I knew set his to 99 (When a 486DX2/66 was the top dog) and told me he was running at 100 MHz, I believed him!

    1. My dad played a prank on my uncle when he got a 486 DX4-100 and swapped the jumpers around between full speed and reduced speed, so the higher number displayed when the computer was throttled. My uncle never caught on – he didn’t notice his bleeding edge super-fast machine was running way too slow, confirming some suspicions we had about how computer literate he actually was.

  2. I’ve never had a personal computer with a Turbo button.

    Not my.KIM-1, not my OSI Superboard II (though I added a jumper and boosted it to 2MHz), not my Radio Shack Color Computers, not my Macs, which by then was no longer early.

    1. The CoCo may not have had a turbo button but it did have POKE 65495,0

      In the era of passive cooling, it was a bit risky. If I remember right it also it messed up the serial port among a few other things as they were based on the CPU speed.

        1. Yes it only increased the CPU clock. There was another POKE command (POKE 65497,0) to change the RAM timings. But it also corrupted the display. Thus you’d be typing blind until you disable it. I never tried that one on actual CoCo hardware.

          Not sure about the CoCo III as I never had the chance to use one. But I heard it’s supporting chipset handled these pokes better.

    2. Those didn’t need it, since they were stuck and didn’t evolve.

      The MS-DOS world was different, sadly.

      Later 1980s applications either assumed an IBM PC 5150 or PC/XT 5160 at 4,77 MHz and no longer the more diverse MS-DOS Compatibles.

      Or in the early 1990s, didn’t take the dramatic processor evolution of the 90s into account. A game that was coded to be as fast as possible in a time of slow processors suddenly ran unplayable fast just a few years later.

      Turbo Buttons fixed that issue or at least calmed it down. If speed drops by 50%, it’s usually enough to be on the safe side.

      Another issue were idle loops. Turbo Pascal 7 had this issue: That over ~200 MHz bug. Several hex editors (say XVI32) have a feature to fix such old DOS binaries.

      Description of the issue:

      1. You miss the point. The article talked about “early personal computers”, and I gave examples of earlier, which had no turbo button.

        Too often the articles here act like a shared experience, but only if yku arrived later.

        1. So you do, I guess. The computers mentioned were learning computers or home computers, not “Personal Computer” to my understanding. The KIM-1 was like a Sharp MZ-40K or a Sinclair ZX80. A little educational “thing” with limited resources and no communications ports (Centronics, RS-232 etc).

          By unwritten rules, a Personal Computer *usually* is a machine capable of of proper word processing, at least. Which involves an text generator with a capability of 80×24, at least. That was the basic standard of glass terminals. And/or a mechanical keyboard.

          And no, just because a computer is a personal property and doesn’t need to be shared with other users (as in the mainframe era) doesn’t make it a “Personal Computer”. A personal computer, maybe, but not a PC. A PC is capable of serious work, business use. Not merely playing Pong, Pac Man or Head over Heels.
          Otherwise a Philips

          G7000/Magnavox Odyssey 2 is a PC, too.

          A home computer capable of 40×25 resolution was barely a Personal Computer, either. Ok, theoretically some could emulate 80 char mode via software – the Commodore C64 did via some public domain program. It also had a real mechanical keyboard, even though it wasn’t great.

          But that’s a gray zone. The Commodore C128, on the other hand, did deserve its name as a Personal Computer. It had a Z80 for CP/M mode, but also more importantly a real 80 chars mode and a graphics board with high-resolution video output (Chroma/Luma aka S-Video).

          Classics like the Commodore PET or the Apple II are more like Personal Computers. They had proper text mode and/or featured expandibility. Also they had been used with professional green monitors and existed with different specs. They were no toy computers/homebrew kits.

          Anyway, I’m just human. And to err is human. If you don’t agree, then that’s fine, as well. Feel free to share your point of view. Maybe we’re both wrong, also. Who knows.

          1. I lived through the era. There was no time when “oh, we’re in the age of personal computers”. It’s marketing, and people who came late wanting to distance themselves from the messy time when you needed to onow things and maybe put things together.

            The Sphere came out in 1975, though it wss never clear how many they sold. The Sol-20 came out in 1976. Both were complete computers. The OSI Superboard, and the encased version the C1P, came out in 1978.

            When the H-11 came out in 1977, Heathkit called it a “personal computer”.

            There’s circular logic here. The VIC-20 and C-64 didn’t have turbo buttons, neither did the Atari ET or the Amiga 500. So you can’t use them as a rebuttal.

            This keeps happening. The stories leave out something, I challenge it, and you in effect tell me I’m wrong.

  3. One of my earliest electronics projects was a 3 digit seven segment display that ran off the parallel port. The driver program I wrote for it took some 10% of CPU just to multiplex the digits, but it was worth it to get some glowing numbers!

      1. By the time the IBM PC emerged, the PC industry was already well-established and millions of people owned PCs. And the “turbo” buttons weren’t didn’t come along until years into the existence of IBM-compatibles.

        That’s what I mean. The Commodore PET and its progenitors would more accurately be called “early PCs.”

    1. If we interpret as meaning actual IBM PC architecture, then that is 40+ years old. The time frame these buttons had was from 5 years until 15 years into that era, so it happened during about the first third, that would from a perspective written in 2022 look like “early”. If writing in 1990, the adjective “early” being a comparative term relating to how much time has passed in a given period, would probably apply only to IBM made PCs and XTs which of course did not have turbo buttons to make them better compatible with lazy programming. A skill frequently required of human adults in mental competency tests is the ability to know what year it is.

      1. “A skill frequently required of human adults in mental competency tests is the ability to know what year it is.”

        That reminds me of the little known CRT test (pun intended). No kidding, it’s really a fascinating thing.

        It’s astonishing also how many people with a self-proclaimed high IQ level apparently struggle here (yes, I confronted people with it that I do personally know).

        The test seems more focused on the intelligence of the mind/personality or its ability to truely think through a given scenario, rather than raw brain power, I think.

        Ironically, the test itself seems more intelligent than the average IQ test, also. The questions inherent some elegance and thoughtfulness that’s missing in the “real” tests, IMHO.


          1. Got a problem with people teaching “Critical Race Theory” Ren? Hope that’s not true… (speaking of the perfect intelligence test). I’d be interested to see how many opponents of *CRT are white, middle-class males.

          2. Ren, I see your comments all the time and I like to think I would like you, but please do some research into critical race theory, it is not what either side is saying it is. Thank you and have a good day

  4. “In days past, this automotive nomenclature implied a performance boost when activated. Instead, ‘turbo mode’ would clock your x86 processor at its rated speed. Disabling ‘turbo’ would throttle the CPU, often all the way down to 4.77MHz. ”

    I remember having one that was either 66MHz or 33MHz, depending on the button state. It impacted some games that would be much easier on 33MHz. Later had something similar, iirc with need for speed 1 or 2, where my new computer wouldn’t run it properly. Everything went way too fast, so fast, you press the up button and the car was crashed by the time you released it. If you could slow down time you could probably do a lap in 3 seconds.

    1. There were different methods for the Turbo Button. Frequency halving (divider), adding wait states, slowing down the ISA bus/the processor front side bus (FSB), switching the primary selection for the oscillators available, using the 14.318 MHz reference crystal for also clocking the whole CPU/Mainboard etc etc.

      In the end, it’s hard to make a generalization here. Some Turbo Buttons really were speeding up if pressed (full speed), while others reacted like brakes if pressed (decreased speed).

      These things solely depended on the motherboard design or the switch type.
      Some switches do cut (open) a connect if pressed, some close it.

      And then there are the motherboards. Some have an inverse logic. If no Turbo Button is attached to the pin header, the board runs normal (full speed). That’s for convenience: No cable with Turbo Button or a jumper is needed here for normal operation. Newer models are like this, afaik.

  5. Modern Intel systems can have a (de)turbo button by having it connect PROCHOT to ground. Did that once for a DIY microserver to substantially reduce the backup power requirements. If the main power goes out of range, the PROCHOT line gets pulled to ground and the CPU is throttled to minimum speed.

  6. My current pc, a z390 chipset from gigabyte, aorus xtreme, came with a little pcb that plugs into a header on the bottom which basically has a few turbo buttons among other things. You can adjust bclock while running too. Can also do the original turbo buttons purpose and knock it down to 800 mhz (few orders of magnitude off but I can’t help but notice the similarity) I forget what the pcb is called sorry

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