Files that are needed to install software and are usually on the CD supplied by the software vendor. For example, the source files for Microsoft Windows NT on an x86-based system are on the Windows NT CD in the \I386 folder, the source files for Microsoft Windows 98 are on the Windows 98 CD in the \Win98 folder, and the source files for Microsoft Windows 2000 are on the Windows 2000 CD in the \I386 folder.
By copying source files from a CD to a folder on a network server and then sharing that folder, you can create a distribution server. A network client can then connect to the distribution server and install the application or operating system without having to use a local CD-ROM drive.