(1) (Serial Digital Interface) A physical interface widely used for transmitting digital video in various formats. For electrical transmission, it uses a high grade of coaxial cable and a single BNC connector with Teflon insulation. It also uses optical fibers with ST, SC and FC connectors. Following are the common digital formats transmitted over SDI. See ITU-R BT.601, BNC connector, fiber-optic connectors and serial interface.

 Standard Definition     Aspect  Transfer
 SD-SDI                  Ratio   Rate

 Digitized NTSC (4FSC)    4:3    143 Mbps
 Digitized PAL (4FSC)     4:3    177 Mbps
 Component ITU-R BT.601   4:3    270 Mbps
 Component ITU-R BT.601  16:9    360 Mbps

 High Definition
 HD-SDI

 Component ITU-R BT.709  16:9  1,485 Mbps

(2) (Switched Digital International) An AT&T dial-up service providing 56 and 64 Kbits/sec digital transmission to international locations.

(3) (Single Document Interface) A Windows function that allows an application to display only one document at a time. SDI requires the user to load another instance of the application to work with two or more documents. Contrast with MDI.

(4) (Standard Drive Interface) A hard disk interface for VAX computers.

(5) (Strategic Defense Initiative) A high-tech defense system for the U.S. proposed during the Reagan administration in the 1980s.