Maybe it needs a reboot in order to de-turbo. I believe some systems don't decrease the speed on-the-fly.

skyfoxxp wrote on 2025-01-13, 16:24:

Hello ! There is no update on this wonderful motherboard so I may add one! I was lucky to get one of this boards with a Pentium […]
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Hello !
There is no update on this wonderful motherboard so I may add one!
I was lucky to get one of this boards with a Pentium 66. Everything works well except from the Turbo Switch : there is a turbo sw header (present and documented) but it doesn't seem to act in any way, even after ensuring that the matching setting in the BIOS is active (turbo switch = Enabled).
Do you experience such a behavior ?
Thanks ! 😀

Could setting it enabled in BIOS actually mean that it is turbo'ed all the time regardless of the switch's position?

Thanks ! I tried both settings (enabled / disabled), no effect.

I could try switching to the Phoenix BIOS (currently this is the Award that is installed). But I don't know which flasher executable to use to do this Award => Phoenix flash update...

PD2JK wrote on 2025-01-13, 21:30:

Maybe it needs a reboot in order to de-turbo. I believe some systems don't decrease the speed on-the-fly.

Yes I tried this as well, no effect whatsoever ! 😀

I had similar situation on a 386 board. Switching the keyboard controller resolved the issue. Howver, only 1 of 6 keyboard controllers I tested allowed the turbo to function correctly.

feipoa wrote on 2025-01-15, 02:34:

I had similar situation on a 386 board. Switching the keyboard controller resolved the issue. Howver, only 1 of 6 keyboard controllers I tested allowed the turbo to function correctly.

That's incredible ! 😉

Hello !
Which BIOS do you use on this motherboard ?
I currently have the Award 12/02/94-SiS-501-503-2A5IAE11-00, but it's not Y2K compatible at all, with the infamous year 2094 bug.

I see that there is a modded BIOS here:
https://theretroweb.com/motherboards/s/ecs-si … o-rev.-1.1#bios

But with no description at all, I'm a bit reluctant to flash it...
Thanks ! 😉

feipoa wrote on 2025-01-15, 02:34:

I had similar situation on a 386 board. Switching the keyboard controller resolved the issue. Howver, only 1 of 6 keyboard controllers I tested allowed the turbo to function correctly.

I eventually managed to find out why the De-Turbo mode is not working as expected :
- Turbo only works when the CPU is in Write-Through mode. (Won't work in Write-Back) => This is configured by the JP19 jumper near the cache modules.
JP19 = 1-2 for Write-back, JP19 = 2-3 for Write-Through.

Norton Sysinfo performance index with a Pentium 60 CPU:
- Write-Back mode : 190 (Turbo or De-Turbo, zero difference)
- Write-Through mode with Turbo : 142 (ouch, that's a huge performance hit !)
- Write-Through mode with De-Turbo : 95.

So practically this is not a good solution to set the write-through mode, since you only get a DX-66ish performance !

EDIT :

I found a way to use the Turbo button by combining both Turbo switch + write-back/through mode.
I proceeded like this:
- I placed a fixed jumper on J16 (turbo switch header of the motherboard)
- I connected the "turbo switch" 3-pin connector cable of the AT case onto JP19 (write-back/through selector).

In this case:
- When the Turbo button of the AT case is in "Turbo" High-speed:
=> The CPU is in write-back mode (fast)
=> The De-turbo mode is ignored, even if J16 is closed
=> Norton Sysinfo gives a score of 190 (normal for a Pentium 60)

- When the Turbo button is in low-speed (De-Turbo)
=> The CPU is in write-through mode (Norton SI 140)
=> The De-Turbo mode is fully active with J16 closed
=> So practically the Norton SI index is 95, exactly half of Turbo mode, equivalent to a 486 at 33-40 Mhz.

I'm quite satisfied of this. 😀