Half duplex is bi-directional communication while taking turns. Floppy disk drives offer removable, rewritable, magnetic storage. Hard disk drives offer non-removable, rewritable, magnetic storage. A hard disk contains several distinct parts. Tracks are concentric circles of data on a given surface.
Sectors are the wedge-shaped divisions of the disk.
Cylinders are a vertical stack of tracks on a hard disk. The IDE and SCSI standard interfaces differ greatly. SCSI supports seven devices with unique IDs and drive termination. They must be rated to handle the amount of power required by all devices it powers. This rating is expressed in watts.