System.Windows.Forms.Timer will execute in the UI thread System.Timers.Timer executes in a thread-pool thread unless you specify a SynchronizingObject System.Threading.Timer executes its callback in a thread-pool thread

The normal timers (system::timers::timer) are not accurate on fast timings. The thread sleep instruction timer also is often not. A minimum resolution may be 15mS or it may 55mS. Also it seems that if you specify a time of say 10mS, this will get rounded up to match the nearest time resolution – basically crap! […]