MS01 is the signature of the tag used by Windows to track the media type. For a more complete discussion of tags and signatures, see the ICC version 3.0. The data size is of type icUInt32Number (an unsigned 32-bit identifier value according to the ICC specification). The purpose of this tag is to identify the current media type that the printer driver is configured for and map it to the appropriate ICC profile. It directly corresponds to the dmMediaType member of the printer driver's DEVMODE structure. It must be an exact match to map correctly. A more detailed discussion of run-time profile selection is given later in this section. If this tag is not defined within the profile, a key value of "MediaUnknown" is placed in the registry at installation time. For a complete description of values for this tag, see the Win32 SDK or Windows 95 DDK documentation about the DEVMODE structure.