Excel Services is part of Microsoft Office SharePoint Server 2007. Excel Services is built on ASP.NET and Windows SharePoint Services 3.0 technologies. There are three core Excel Services components:
Excel Services handles communication among the three components and load-balances the requests made to Excel Calculation Services.
The Excel Web Access, Excel Services, and Excel Calculation Services components can be divided into two major groups: the components on a front-end server (also known as the “Web front end”), and the component on a back-end application server.
In multiple-server configurations, Excel Services load-balances requests across multiple Excel Calculation Services occurrences in a farm configuration. If your installation includes multiple application servers, Excel Services will balance the load to ensure that no single application server is overloaded by requests. Administrators can configure the load-balancing behavior.
Web Front-End and Back-End Application Servers
The Excel Web Access, Excel Services, and Excel Calculation Services components can be divided into components on the Web front-end server and those that live on a back-end application server. The Web front end includes Excel Web Access and Excel Web Services. The Excel Calculation Services component resides on the back-end application server, alongside any user-defined function assemblies that an administrator may have added.