Microsoft Terminal Server is a component of the Windows operating system that allows users to remotely access servers and applications over the internet or a local area network. Terminal Server runs on Windows Server 2003, Windows 2000 Server and Windows NT 4 Terminal Server. Client devices connecting to a Terminal Server can be Windows workstations, Macintosh or Linux machines, mobile devices and dumb terminals.

When Terminal Server is installed and enabled on a Windows Server, users can connect to virtual desktops, or single instances of an application. User's applications, or virtual desktops, are executed on the server instead of the client. The end user sees their terminal services session across the network or internet connection, similar to VNC or Citrix.

Unlike these other remote control programs, a Windows Terminal Server runs a in a multi user mode that allows multiple users to log into the server at the same time. Depending on the hardware and resources that the server can provide, a single Terminal Server can support dozens or even hundreds of simultaneous users.

Terminal Server sessions provide support for many client side resources. For example, a Windows 2003 Terminal Server supports accessing your local disk drives, printers, serial ports, sound and the windows clipboard while connected to a Terminal Services session.

The Windows XP Pro operating system also provides similar functionality. It is called "Remote Desktop". The main difference is that it only supports one user at a time. If you connect to a Windows XP Pro machine via a Terminal Services session, it will actually lock the console of the physical machine. "Remote Desktop" can be enabled on an XP Pro machine by accessing the "System" applet, selecting the "Remote" tab and checking the option that says "Enable Remote Desktop on this computer".

Building a stable Terminal Server solution can be a lot of work, and this article merely scratches the surface of the technology, but hopefully you now have a better idea of what it is and what it can do.