LGR - PC Turbo Buttons
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Date: 2022-04-14
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Comments and reviews: 10
C64
There is actually much more important reason for the turbo button.
Standard TTL logic limits the speed of the ISA bus to 8MHz. So when CPUs became faster, there was a problem. The clock speed had to be divided on the ISA bus. So the CPU has to stop and wait for a clock cycle on the ISA bus to read a register on this bus.
But worse, if your CPU is e. g. 10 MHz, the ISA bus runs with half the speed which is 5MHz in this example. If the CPU is faster then 16 MHz, the ISA bus must run with a quarter of this speed since you need to divide 2 times by 2.
The TURBO switch sets the CPU to 8MHz so the ISA bus can run with full speed and the CPU never has to stop and wait.
So while the original TURBO slows down your CPU, it speeds up the ISA bus which gives your hardware the maximum performance. This is why the original TURBO seemed to work the other way round. Depending on your CPU speed, you get a lot more data transfer by using TURBO so faster graphics, HDD, network and so on. While rendering graphics was slower due to slower CPU speed, displaying e. g. a BMP from the HDD was quicker.
More important was controlling hardware like CNC machines through ISA cards. With the TURBO on, you have much more performance and full control over the timing.
When the VESA Local Bus came, you could run the cards with the CPU speed above 8MHz so it made more sense to think the other way round and make the TURBO switch speed everything up. Your plain ISA cards then could become a lot slower when the TURBO was activated depending on the dividing factor necessary for your CPU max speed.
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There is actually much more important reason for the turbo button.
Standard TTL logic limits the speed of the ISA bus to 8MHz. So when CPUs became faster, there was a problem. The clock speed had to be divided on the ISA bus. So the CPU has to stop and wait for a clock cycle on the ISA bus to read a register on this bus.
But worse, if your CPU is e. g. 10 MHz, the ISA bus runs with half the speed which is 5MHz in this example. If the CPU is faster then 16 MHz, the ISA bus must run with a quarter of this speed since you need to divide 2 times by 2.
The TURBO switch sets the CPU to 8MHz so the ISA bus can run with full speed and the CPU never has to stop and wait.
So while the original TURBO slows down your CPU, it speeds up the ISA bus which gives your hardware the maximum performance. This is why the original TURBO seemed to work the other way round. Depending on your CPU speed, you get a lot more data transfer by using TURBO so faster graphics, HDD, network and so on. While rendering graphics was slower due to slower CPU speed, displaying e. g. a BMP from the HDD was quicker.
More important was controlling hardware like CNC machines through ISA cards. With the TURBO on, you have much more performance and full control over the timing.
When the VESA Local Bus came, you could run the cards with the CPU speed above 8MHz so it made more sense to think the other way round and make the TURBO switch speed everything up. Your plain ISA cards then could become a lot slower when the TURBO was activated depending on the dividing factor necessary for your CPU max speed.
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LGR
To clarify further: the turbo button _does not_ overclock your CPU or make it go faster than its intended speed. Even if pressing your turbo button made things faster, that just meant it was allowing you to use your normal CPU speed. The initial function of the turbo button is just a matter of which method the PC booted up in: turbo enabled or disabled. This is what I talked about with the BIOS settings at 03: 15.
It made sense to have the default boot setting be -turbo disabled- for most manufacturers, because otherwise you'd have lots of people using their computer at a slower speed all the time, not knowing they had to press the turbo button to run with the advertised performance!
Turbo buttons are no longer needed because programmers stopped designing software that depended on clock speed to run correctly, and people by and large stopped using older software that still did. There are exceptions to this of course, but for the most part the turbo button ceased being a requirement due to popular software of the late-90's running fine on any CPU. Nowadays, there are games that depend on frame rates to run their physics correctly, but this is another issue entirely.
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To clarify further: the turbo button _does not_ overclock your CPU or make it go faster than its intended speed. Even if pressing your turbo button made things faster, that just meant it was allowing you to use your normal CPU speed. The initial function of the turbo button is just a matter of which method the PC booted up in: turbo enabled or disabled. This is what I talked about with the BIOS settings at 03: 15.
It made sense to have the default boot setting be -turbo disabled- for most manufacturers, because otherwise you'd have lots of people using their computer at a slower speed all the time, not knowing they had to press the turbo button to run with the advertised performance!
Turbo buttons are no longer needed because programmers stopped designing software that depended on clock speed to run correctly, and people by and large stopped using older software that still did. There are exceptions to this of course, but for the most part the turbo button ceased being a requirement due to popular software of the late-90's running fine on any CPU. Nowadays, there are games that depend on frame rates to run their physics correctly, but this is another issue entirely.
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TheSteelRodent
I have a computer case from the machine I bought in 1996 (a Pentium 75) and it doesn't have a turbo button, but it does have a turbo LED and I never understood why, because by then PCs had no way of changing the clock speed without setting jumpers on the motherboard.
But although the turbo button indeed was meant to half the clock speed, I have come across machines that would boot in the slow speed and pressing the turbo button would switch them to full speed. My brother's 286 AT-clone had a keyboard shortcut you could press to toggle between clockspeeds (think it was 8/10/12/16 or something like that, but it would always crash almost immediately when we tried to run it at the highest speed. Think it also had a turbo button, but I don't recall it working on that machine.
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I have a computer case from the machine I bought in 1996 (a Pentium 75) and it doesn't have a turbo button, but it does have a turbo LED and I never understood why, because by then PCs had no way of changing the clock speed without setting jumpers on the motherboard.
But although the turbo button indeed was meant to half the clock speed, I have come across machines that would boot in the slow speed and pressing the turbo button would switch them to full speed. My brother's 286 AT-clone had a keyboard shortcut you could press to toggle between clockspeeds (think it was 8/10/12/16 or something like that, but it would always crash almost immediately when we tried to run it at the highest speed. Think it also had a turbo button, but I don't recall it working on that machine.
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fanjoy
I just like how on many models, the Turbo button was often found close to the Reset button. I remember a few times accidentally hitting the wrong button and losing whatever I was doing (usually playing a game or something. I mean, they really should have put the button elsewhere, maybe by the power switch or something. To this day, I never connect reset switches in modern computers anymore. Partially because they are pointless IMO these days. On the older systems (older AT systems) I would actually disable the reset switch in most cases anyway, partially so I didn't accidentally hit it and lose work and because again, it was pointless. If the computer locked up you just switched it off and back on.
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I just like how on many models, the Turbo button was often found close to the Reset button. I remember a few times accidentally hitting the wrong button and losing whatever I was doing (usually playing a game or something. I mean, they really should have put the button elsewhere, maybe by the power switch or something. To this day, I never connect reset switches in modern computers anymore. Partially because they are pointless IMO these days. On the older systems (older AT systems) I would actually disable the reset switch in most cases anyway, partially so I didn't accidentally hit it and lose work and because again, it was pointless. If the computer locked up you just switched it off and back on.
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arsenic1987
When we grew up, we all had different opinions on what the TURBO actually -did-. We somehow never played games at that exact time the 4. 77 was the norm. To a kids' mind, we couldn't really see any difference, so there became so many different theories among our friends on what it actually did.
Some of us actually used it while playing games like StarCraft 1, thinking that it was -tampering- with the times it took to build stuff. I vividly remember a LAN we had where some were pressing the turbo button over and over while playing stuff. Now, they MIGHT have had 4. 77 processors in a turbo case, but still. That little LED showing -Turbo active- was really a venture for us: )
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When we grew up, we all had different opinions on what the TURBO actually -did-. We somehow never played games at that exact time the 4. 77 was the norm. To a kids' mind, we couldn't really see any difference, so there became so many different theories among our friends on what it actually did.
Some of us actually used it while playing games like StarCraft 1, thinking that it was -tampering- with the times it took to build stuff. I vividly remember a LAN we had where some were pressing the turbo button over and over while playing stuff. Now, they MIGHT have had 4. 77 processors in a turbo case, but still. That little LED showing -Turbo active- was really a venture for us: )
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Dahcrazychicken
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Yarnosh
Blows my mind that someone decided to build such a specialized function into the hardware rather than just declare those old games unsupported or incompatible. It's become kind of the M. O. on PC though. to bend over backwards to retain compatibility with obscure old software. often at the expense of modern software (indirectly. Look at how long DOS dominated the PC OS scene. It was an operating system compatible with the first 8086 PC XT. surviving well into the 1990's. There was a time when I ran MSDOS as the primary OS on a 80486! That's insane to me now. I actually cared about -conventional memory- on a 486.
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Blows my mind that someone decided to build such a specialized function into the hardware rather than just declare those old games unsupported or incompatible. It's become kind of the M. O. on PC though. to bend over backwards to retain compatibility with obscure old software. often at the expense of modern software (indirectly. Look at how long DOS dominated the PC OS scene. It was an operating system compatible with the first 8086 PC XT. surviving well into the 1990's. There was a time when I ran MSDOS as the primary OS on a 80486! That's insane to me now. I actually cared about -conventional memory- on a 486.
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CDP1861
Look at it from a seller's perspective. If you have two identical computers, but the button on one is labeled 'Turbo', the other has it labeled 'Slow'. It's just semantics, but which one of the two would the customers find more attractive? The same goes for the 7 segment displays. You can jumper these things to display any two numbers. The clock frequency is not really measured. I wonder how often that has been used to pull some more money out of the customer's pockets.
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Look at it from a seller's perspective. If you have two identical computers, but the button on one is labeled 'Turbo', the other has it labeled 'Slow'. It's just semantics, but which one of the two would the customers find more attractive? The same goes for the 7 segment displays. You can jumper these things to display any two numbers. The clock frequency is not really measured. I wonder how often that has been used to pull some more money out of the customer's pockets.
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LegoTekFan486
Someone should make a mainboard with headers for extra buttons and indicator lights for geeky control panels on the front of the case. The lights could be configured via some software tool to come on when X, Y or Z occurs, and the buttons could be configured using the same tool to do whatever, including activate overclock, switch lighting modes or what have you.
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Someone should make a mainboard with headers for extra buttons and indicator lights for geeky control panels on the front of the case. The lights could be configured via some software tool to come on when X, Y or Z occurs, and the buttons could be configured using the same tool to do whatever, including activate overclock, switch lighting modes or what have you.
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Luis
I remember the days of pin configuration in the case for the display to show one -clock speed- with turbo button pushed and another when not, right until clockspeeds did not longer fit in the displays so it had to be pinned to -hi- and -lo-. and then one day no more display in the case nor turbo button (that once connected to the MB and display, then only to the display)
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I remember the days of pin configuration in the case for the display to show one -clock speed- with turbo button pushed and another when not, right until clockspeeds did not longer fit in the displays so it had to be pinned to -hi- and -lo-. and then one day no more display in the case nor turbo button (that once connected to the MB and display, then only to the display)
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