I have an opti 386 / 486 board that does this. Once EMM386 is installed then only re-booting the machine will allow the motherboard to change the turbo setting. I made the same assumption as you, something to do with virtual mode.

I like it, because it's actually changing the clock speed, and not just turning off the cache.

Thanks man for the answer.

Thing is this board actually gets very slow when Turbo is disabled. I think not only it lowers clock speed it also disables the cache. According to NSSI software the system gets slower than a 286 @ 16MHZ. I was expecting it would slow it to the level of a 386 DX 16 or even a DX 20.

I gotta test it more. Is there any software tool that allows to enable/disable cache via DOS prompt? That way i could check if it is disabling the cache and i could enable it back if i need slight more performance.

I would think that most games that use EMM386 would not run very playably if the turbo is off.

If i disable the cache in my system, performance is between a 386 DX-25 and a 386 DX-33. This is perfect to play Wing Commander. Great, with this system i can pretty much achieve several different system speeds.

I have a clone 386 with an Intel DX33. My turbo switch works instantly with emm386 or not, in DOS or Windows 3.1. I can be playing wing commander in a dogfight and it switches instanly during gameplay. My board is running 33 mhz with turbo and 8 mhz with it off.