Turbo button on Pentium systems

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Turbo button on Pentium systems

Postby Nprod » 2018-2-04 @ 22:52

Hello! I've been trying to find out some info on the Turbo function on old boards and figured this would be the best place to ask. Does such a feature exist on Pentium systems or is it strictly a "486 and older" thing?

I've had the chance to mess around with a couple of boards recently and while they do have TB-SW pins on the header, connecting them seems to just halt/pause the system instead of performing an underclock. It's like AT cases from that era often have the button and LED display but it's just decorative and doesn't really do anything. One of the boards (PCchips M571) has a "slow clock ratio" setting in bios but there's really no apparent difference from changing the setting. I've also seen "workarounds" where people hook up the button to one of the CPU multiplier jumpers, but is that a safe way to do it? Can you toggle the multiplier while the system is running or does it requre a restart?

Hope someone more knowledgable can clue me in on this.
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Re: Turbo button on Pentium systems

Postby The Serpent Rider » 2018-2-04 @ 23:09

Some early pentium boards with socket 4/5.
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Re: Turbo button on Pentium systems

Postby kaputnik » 2018-2-04 @ 23:17

Pentium systems usually still has something called "turbo feature", however, I've never encountered one that works like ditto on 486 systems and earlier, and slows the system down to 8088 speeds. It sets the FSB to 50 MHz, and nothing else. You do the math. The slowdown is not enough to even have practical use to speak of.

Not 100% sure, but my guess is that closing the turbo jumper does the same thing electrically as jumpering the board for 50 MHz FSB.

Toggling the switch while the system is running won't do anything, but should probably be avoided anyways. Guess the FSB speed is set very early in the boot process.
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Re: Turbo button on Pentium systems

Postby Nprod » 2018-2-04 @ 23:28

kaputnik wrote:Pentium systems usually still has something called "turbo feature", however, I've never encountered one that works like ditto on 486 systems and earlier, and slows the system down to 8088 speeds. It sets the FSB to 50 MHz, and nothing else. You do the math. The slowdown is not enough to even have practical use to speak of.


So you're saying that disabling the cache in BIOS is the more practical way to do it with these systems. What got me curious was that "sclow clock ratio" option in the power management settings - you can choose anything from "1/1" to "1/128" but maybe it's just some sort of low-power mode instead of a proper underclock.
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Re: Turbo button on Pentium systems

Postby jheronimus » 2018-2-04 @ 23:36

The most useful turbo I have on a Pentium board is on an Intel’s own Batman’s Revenge (Pentium 60, Socket 4). Turbo slows down the P60 to something like a 386@33 — good enough to play Wing Commander.

I also have a 430VX board (Lucky Star LS-P54CE) with working turbo, but I think it just slows down the FSB from 66 to 50 or something, so not terribly useful.
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Re: Turbo button on Pentium systems

Postby The Serpent Rider » 2018-2-05 @ 01:09

I think some 486 boards can't do it properly too.
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Re: Turbo button on Pentium systems

Postby Baoran » 2018-2-05 @ 02:45

I have one socket 5 motherboard that actually disables cache when turbo is disabled. It is easy to see because disabling cache in bios doesn't slow down the pc at all when turbo is disabled.
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Re: Turbo button on Pentium systems

Postby kaputnik » 2018-2-05 @ 08:53

Nprod wrote:
kaputnik wrote:Pentium systems usually still has something called "turbo feature", however, I've never encountered one that works like ditto on 486 systems and earlier, and slows the system down to 8088 speeds. It sets the FSB to 50 MHz, and nothing else. You do the math. The slowdown is not enough to even have practical use to speak of.


So you're saying that disabling the cache in BIOS is the more practical way to do it with these systems. What got me curious was that "sclow clock ratio" option in the power management settings - you can choose anything from "1/1" to "1/128" but maybe it's just some sort of low-power mode instead of a proper underclock.


Well, I'd get a Pentium [MMX] with the TR12 registers instead. They can be manipulated from software, to tune the CPU speed in quite fine grained steps. Have a look here. It can of course be combined with disabling L2 from BIOS, got some memory of speedsys scores below 10 with all Setmul TR12 switches and L2 disabled :)

Never seen that "slow clock ratio" BIOS option, but if it's in the APM settings, I'd assume it has something to do with temperature throttling or some power saving state. Might be useful for our purposes, if there's a way to manually set the processor in that mode, and the computer otherwise is fully functional in it.
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Re: Turbo button on Pentium systems

Postby jesolo » 2018-2-06 @ 19:25

I recently acquired a Pentium 120 MHz based system that has an Epox P55-TH Socket 7 motherboard (the motherboard utilises the Intel 82430HX chipset).
Although the motherboard has a Turbo LED header, there is no Turbo switch header on the motherboard.
However, via the keyboard shortcut (Ctrl & Alt & + and Ctrl & Alt & -) this system did actually slow down to the equivalent speed of around a 486DX 33 MHz.
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Re: Turbo button on Pentium systems

Postby Nprod » 2018-2-08 @ 10:49

jesolo wrote:I recently acquired a Pentium 120 MHz based system that has an Epox P55-TH Socket 7 motherboard (the motherboard utilises the Intel 82430HX chipset).
Although the motherboard has a Turbo LED header, there is no Turbo switch header on the motherboard.
However, via the keyboard shortcut (Ctrl & Alt & + and Ctrl & Alt & -) this system did actually slow down to the equivalent speed of around a 486DX 33 MHz.


So i guess the consensus is that around the Pentium I era is where manufacturers stopped caring much about underclocking for the sake of compatibility. I guess slowing it down to 486DX levels isn't too useful, i remember trying to play Worm War for Win 3.11 on a pre-Pentium machine and it still being way too fast to be playable. In any case, would be good to check if the SiS 5571 chipset on this board has this feature.
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Re: Turbo button on Pentium systems

Postby derSammler » 2018-2-08 @ 10:53

jesolo wrote:Although the motherboard has a Turbo LED header, there is no Turbo switch header on the motherboard.
However, via the keyboard shortcut (Ctrl & Alt & + and Ctrl & Alt & -) this system did actually slow down to the equivalent speed of around a 486DX 33 MHz.

All mainboards with a turbo LED but no switch do that. Hotkeys vary, however. I guess there was no other way, as case manufacturers stopped providing a turbo switch at some time.
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Re: Turbo button on Pentium systems

Postby Scali » 2018-2-08 @ 12:11

Nprod wrote:I've also seen "workarounds" where people hook up the button to one of the CPU multiplier jumpers, but is that a safe way to do it? Can you toggle the multiplier while the system is running or does it requre a restart?


I did that on my Pentium 133. It's safe in the sense that nothing happened. You had to restart the system (reset or power cycle) before it would take on the new multiplier value. It was apparently never designed to switch on-the-fly, unlike the turbo on 8088-486 systems.
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Re: Turbo button on Pentium systems

Postby Scali » 2018-2-08 @ 12:13

The Serpent Rider wrote:I think some 486 boards can't do it properly too.


Yup, I have a Compaq Deskpro XL466, a very late 486DX2-66 (from the Pentium Pro era), and it has no turbo switch anywhere. As far as I know there is no keyboard combination or BIOS setting to change the speed either (it's basically a 486 CPU-board in a Pentium Pro case and motherboard).
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Re: Turbo button on Pentium systems

Postby j^aws » 2018-2-10 @ 02:08

Nprod wrote:Hello! I've been trying to find out some info on the Turbo function on old boards and figured this would be the best place to ask. Does such a feature exist on Pentium systems or is it strictly a "486 and older" thing?

Yes, they do exist, even on Socket 7. For example:
viewtopic.php?f=25&t=53479
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