This Fast/Slow option determines how quickly you’ll get Windows 10 updates. Although the Windows 10 Technical Preview is unfinished software, and should be treated as such, Microsoft knows that some business and consumer customers want to test the operating system, but not necessarily be on the bleeding edge. Those customers can therefore set this update frequency option to “Slow,” and Microsoft will only release updates that have been tested to a relatively good degree. Those who want all the latest features right away, including potential bugs that could wipe out data, should choose “Fast.”
When it comes to DC motors, however, there is a very interesting effect while using this decay mode. While on fast decay mode the DC motor rotor coasts down in speed, with slow decay mode the rotor stops very quickly. This is because as can be seen by the above picture, you are shorting the DC motor terminals. This in essence implies the BACK EMF voltage source inside the motor to be shorted. And if there is no BACK EMF, there can be no speed. One is directly tied to the other. We call this phenomenon braking the DC motor or the collapse of the Back EMF. Braking is vital when you want to stop your motor very fast and possibly obtain a particular position. With coasting, this would not be possible, so be aware that selecting slow decay or fast decay with DC motors is not a trivial endeavor.