Revit 2012 is set to 'include' the Revit Server, meaning it will no longer be a subscription item, it will be built in to the Revit 2012 install.
What is the Revit Server?
Revit Server is the server application for Revit Architecture, Revit Structure, and Revit MEP. It is the foundation for server-based worksharing for Revit projects. A workshared project is a Revit building model that multiple team members can access and modify at the same time. Revit Server uses a central server and multiple local servers for optimal project collaboration across a wide area network (WAN).
Central server: A server that is accessible to all team members over the WAN. When you enable worksharing for a Revit project, you can place the central model on the central server. The central server hosts the central model of a workshared project.
Local server: A server that is accessible to all team members in a local area network (LAN). The local server hosts a local, up-to-date copy of the central model. Team members are typically unaware of the local server because it is transparent in their daily operations.
How does the Revit Server work?
The Revit Server network architecture consists of a single central server that connects with multiple local servers.
Upon opening a server-based workshared project, a team member is working in a local copy of the central model. This local copy, called the local model, is stored on the team member's computer. The central model is stored on the central server.
As a team member works, the local server silently requests updated information from the central model on the central server, using available network capacity to transfer data over the WAN. The updated version of the model is stored on the local server, so the updates are readily available when a team member requests them.
Reload Latest: When a team member starts Reload Latest, the local model is updated with information that is already stored on the local server. In addition, the local server makes another request to the central server for any additional updates. Because much of the updated information already resides on the local server, the local model is updated quickly. The team member does not need to wait for all of the update information to be transferred over the WAN.
Synchronize with Central: When a team member starts Synchronize with Central, a Reload Latest operation updates the local model with changes made by other team members. The central model is also updated to reflect changes made to the local model. First, the current version of the local model is saved on the local server. Then the local server sends that data to the central server.