Explain the architecture of the Excel Services?

Excel services is built on ASP.NET and Microsoft Windows Sharepoint technologies.
The main components of Excel Services include :
1.    Excel Web Services
2.    Excel Web Access[EWA]
3.    Excel Calculation Server [ECS]
They are basically grouped into two layers :
1.    The Web Front End [WFE] where Excel Web Access [EWA] and Excel Web Services [EWS] reside.
2.    The application server where Excel Calculation Server [ECS] resides and where all the calculations are made.