An early disk cartridge was a single hard disk platter encased in a protective plastic shell. When the removable cartridge was inserted into the cartridge drive peripheral device, the read/write heads of the drive could access the magnetic data storage surface of the platter through holes in the shell. The disk cartridge was a direct evolution from the disk pack drive, or the early hard drive. As the storage density improved, even a single platter would provide a useful amount of data storage space, with the benefit being easier to handle than a removable disk pack. An example of a cartridge drive is the IBM 2310. Disk cartridges were made obsolete by floppy disks.
Some more recent removable disk storage media are referred to as disk cartridges. This is most common with Zip disks. It is very rare, but not unheard of, to refer to the 3½-inch microfloppy as a disk cartridge.
Some types of optical discs and magneto-optical discs were either permanently enclosed in a protective plastic sheath, or placed into a sheath before being inserted into the drive. This sheath was often called caddy, but sometimes also disk cartridge.