Fixed media storage units

**Includes:** - hard disk drives and other storage units where the storage media is physically inseparable from its reading or writing device

**Excludes:** - disk storage units, removable, cf. 45272 - magnetic tape storage units, removable, cf. 45272 - compact disk drives and DVD drives, cf. 45272 - solid-state, non-volatile data storage devices, "flash memory cards" or "flash electronic storage cards", cf. 47550