Backwards Compatibility – How To Speed Up or Slow Down Old 3D Games

Modern CPUs usually change their clock speed based on CPU load in the default setting. You might be able to use the Power item in the Windows Control Panel to switch the power scheme from the default Balanced scheme to Energy Saver. That should lock your CPU to its lowest clock speed.

You can use something like CPU-Z to monitor the clock speed to see if your CPU actually clockspeed changes when you change the powerscheme.

I have actually used this technique to play Commandos. Normally my CPU would switch into performance mode (all 4 cores at 3.2GHz) and the game would run too fast, making it hard to play. After setting the Windows Powerscheme to Energy Saver (all 4 cores on 800Mhz - 1 quarter of full speed) the game would run at the correct speed.

Edit: About using a Virtual Machine:

Virtualbox has the ability to limit the virtual CPU to a percentage of the host CPU, see CPU execution cap in the Processor Settings section. The manual does note that limiting the CPU this way may induce timing problems in the guest, which isn't what you want for older games obviously. Another problem with virtual machines is that hardware acceleration for graphics is still not very well supported, so that limits the usage of VMs for games quite a bit.

I have tried this with Commandos for instance, but the result was not playable. That's when I switched to the technique above to limit the speed of my CPU via Windows Powerscheme.

Good Old Games is a great place to buy older PC games, they're all DRM-free and patched/modified to run on modern OSes. The community is also great in general, and a lot of the game reviews are very well-written. They have a new feature too that lets people set up "GOG mixes" which are basically groups of games, so if you can find one including games you already like, you'd probably like any others in the same group.