Before capturing a disk image using capturing or imaging software, you have to prepare a target computer for the capturing process. The preparation process, which involves generalizing a Windows operating system installation, removes the Security Identifier (SID) so that its installation can be captured as an image and deployed to different computers. An SID is a variable length value that's used to uniquely identify a Windows server or Windows Client installation (a computer), a user, a group, or the owner of an object. When joining a domain, each computer gets its own unique SIDs. When you clone a computer, the SID is cloned as well. This is where problems might occur if the installation is not prepared or generalized, because the domain controller needs to identify the computers uniquely. After a computer has been prepared, you can capture an image of the prepared computer and use it in deployment.