Team Foundation Server (TFS) consists of data tier, application tier and client tier.

TFS's data tier
is hosted by using SQL Server 2005. When you installed TFS, it will create few databases in the SQL Server to store the related data. Databases created by TFS are including:
1. TFSIntegration, which is used to store TFS Core services like project metadata, notifications, security groups...
2. TFSWarehouse is the TFS data warehouse
3. TFSWorkItemTracking is the database used to store the work item tracking in TFS
4. TFSWorkItemTrackingAttachments is the TFS work item tracking attachment database
5. TFSVersionControl is the version control database
6. TFSActivityLogging is the version control event log database
7. TFSBuild is database used to store team build data, like the results, code coverage, test results....

TFS's application tier
is composed of ASP.net web services. The web services installed by TFS include:
1. <install path>\WebService\Services - which are the Application Programming Interface (API) for the TFS core services
2. <install path>\WebServices\VersionControl and <install path>\WebServices\VersionControlProxy - is the API for TFS Version Control
3. <install path>\WebServices\Build - API for Team Build
4. <install path>\WebServices\Warehouse - API for TFS Data Warehouse
5. <install path>\WebServices\WorkItemTracking - API for Work Item Tracking

TFS's client tier
this tier is including the Visual Studio 2005, Microsoft Office Excel, Microsoft Office Project, Microsoft Internet Explorer and Team Exploerer