What is a digital video disk?

VERA (1952) - 2 inch Quadruplex videotape (1956) - 1 inch type A videotape (1965) - U-matic (1969) - Video Cassette Recording (1972) - V-Cord (1974) - VX (aka "The Great Time Machine") (1974) - Betamax (1975) - 1 inch type B videotape (1976) - 1 inch type C videotape (1976) - VHS (1976) - Video 2000 (1979) - VHS-C (1982) - M (1982) - Video8 (1985) - MII (1986) - D1 (1986) - S-VHS (1987) - D2 (1988) - D3 (1991) - D5 (1994) - Digital-S (D9) (199?) - Hi8 (199?) - S-VHS-C (19??) - W-VHS (1994) - DV (1996) - HDCAM (1997) - D-VHS (1998) - Digital8 (1999) - HDV (2003)