The open source tool DxWND can be used to play (mostly older) games in windows mode and has also other tweaks to let games run better on a modern machine. Does anybody here use it and also reduces the demand for cpu cycles? It runs the game I use (Pacific General from GOG) but one hyperthread under full lot and that's annoying because the fan has to do some work. There is a 'Timing' tab, but both frame limiting and time stretching doesn't bring the cpu level down? Has anybody ideas how to achieve this without slowing down all hyperthreads or other programs and manually identifying a thread and configuring it? Thank you.

Open task manager and right click on the task, then "Set Affinity". From there you can restrict the number of cores available to the process. You can modify the program's shortcut to do this automatically by using the Windows "START" command. If you've never used it before, just hit up Google or Youtube for tips.

Hope this helps.

You could try the slowdown tool cpukiller which supports Hyperthreading.

It already uses only one hyperthread. Quote from the web site: So the total CPU load would remain, that's not what I am looking for.

I know, but still worth a try, since occupancy doesn't necessarily mean load. You can occupy resources without stressing the components. At least that's how I would have implemented it, otherwise it'd be rubbish.