When I use the Microsoft Management Console (MMC) Active Directory Users and Computers snap-in to create a computer account on Windows Server 2003, Windows displays a Managed dialog box that has a This is a managed computer option and a field for entering the computer's unique ID. What's a managed computer?
Figure 1 shows the Managed dialog box that you refer to. Managed computers are computers that you set up by using Windows 2003's Remote Installation Services (RIS). A RIS server lets you simply connect a new computer to your network and turn it on; the computer automatically finds the RIS server and starts installing Windows according to the installation profile you set up on the RIS server.
For a system to function as a managed computer, the manufacturer must have assigned the computer a globally unique identifier (GUID), also known as a universally unique identifier (UUID). The concept is similar to how a unique media access control (MAC) address is embedded on each network card. The GUID lets RIS respond with the right Windows installation for the computer.
—Randy Franklin Smith