I found one interesting thing. Windows really runs Main Thread with 16 ms period. But in one case it is not true. I tested WPF application and found out that when I run my app from the Visual Studio debugger the period is getting shorter - about 3 ms! When I run app directly - the period is again 16 ms. My app has one button and ButtonClick() handler. After I click the button I receive the result: 17:32:29.5716958 17:32:29.5735801 17:32:29.5746377 17:32:29.5756864 17:32:29.5777097 17:32:29.5796714 17:32:29.5816662 Can someone figure out how Visual Studio debugger can force shorter Main Thread period for the debugging app?