controlling number of processor cores on your machine

More details on how to do this on various OSes here

1. Go to run (Windows + R button)
2. type msconfig
3. press enter for MSConfig

   

4. In boot click Advanced options.. button
5. Check Number of Processors and pick the count

   

6. reboot

After rebooting if you bring up task manager, it will show only one processor instead of usual 4/8:

If you want to revert back to old setting, just uncheck the Number of Processors check box from step 5 and reboot: