HD

(1) (High Definition) Typically refers to high-definition digital video (for details, see HDTV and DTV). In the past, HD referred to several proprietary high-resolution video formats, both analog and digital, that exceeded the resolution of analog TV (NTSC, PAL). See high-def video formats, HD Radio, HD Audio and HDV.

(2) (Hard Disk or Hard Drive) The HD acronym is widely used in drive specifications; for example, 500GB HD means 500 gigabyte hard disk. FD means floppy disk. See magnetic disk.

(3) (High Density) The official designation for the most common floppy disk formats. For example, the 1.44MB 3.5" floppy was HD in contrast to the earlier double density (DD) 720KB format. For 5.25" floppies, the 1.2MB version was HD; the earlier 360KB was DD. See floppy disk.

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Hip dysplasia.