Two different builds of each NT-based operating system exist:
- The free build (or retail build) of Windows is the end-user version of the operating system. The system and drivers are built with full optimization, debugging asserts are disabled, and debugging information is stripped from the binaries. A free system and driver are smaller and faster, and it uses less memory.
- The checked build (or debug build) of Windows serves as a testing and debugging aid. For details, see checked build.
Distribution media containing the free build of the operating system do not have any special labels — in other words, the CD containing the free build will just be labeled with the Windows version name, and no reference to the type of build.