http://paladinprogram.blogspot.tw/2013/09/rdlc.html

The .NET Framework Class Library includes four classes named Timer, each of which offers different functionality: 

•System.Timers.Timer, which fires an event and executes the code in one or more event sinks at regular intervals. The class is intended for use as a server-based or service component in a multithreaded environment; it has no user interface and is not visible at runtime. 
使用於server-based or service component的多執行緒環境中, 無UI.
使用方式: event message.
  循環時間固定. 不受Job thread影響. 只要時間一到就會呼叫ElapsedEventHandler一次.
  可指定首次執行前的等待時間.  

•System.Threading.Timer, which executes a single callback method on a thread pool thread at regular intervals. The callback method is defined when the timer is instantiated and cannot be changed. Like the System.Timers.Timer class, this class is intended for use as a server-based or service component in a multithreaded environment; it has no user interface and is not visible at runtime. 
使用於server-based or service component的多執行緒環境中, 無UI.
使用方式: callback method.
  循環時間固定. 不受Job thread影響. 只要時間一到就會呼叫callback method一次.
  可指定首次執行前的等待時間.

•System.Windows.Forms.Timer, a Windows Forms component that fires an event and executes the code in one or more event sinks at regular intervals. The component has no user interface and is designed for use in a single-threaded environment; it executes on the UI thread. 
使用於Windows.Form
使用方式: component from toolbox or code.
  跟form同一個執行緒.
  循環時間為(Timer interval + job執行時間). 若Job執行時間超過Timer Interval時間, 則循環執行時間不固定.

•System.Web.UI.Timer, an ASP.NET component that performs asynchronous or synchronous web page postbacks at a regular interval. 
使用於ASP.NET
使用方式: Web page postback.
  可定時以非同步方式更新網頁之UpdatePanel至client端.