Electric power that is provided by an alternate source and that serves as backup for the primary power source at the station main bus or prescribed sub-bus.
Note 1: An offline unit provides electrical isolation between the primary power source and the critical technical load whereas an online unit does not.
Note 2: A Class A power source is a… (Read More →)

1. Storage that is available to a processor only through its input/output channels.
2. In a computer, any storage that is not internal memory, i.e., is not random access memory (RAM).
Note: Examples of auxiliary storage media are magnetic diskettes, optical disks including CD ROM, and magnetic tape cassettes.

Audio Video

1. The degree to which a system, subsystem, or equipment is operable and in a committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time.
Note 1: The conditions determining operability and committability must be specified.
Note 2: Expressed mathematically, availability is 1 minus the unavailability.
2. The ratio… (Read More →)

1. In voice, video, or data communications, a circuit between two points that is ready for service, but is in the idle state.
2. In facsimile transmission, the portion of the scanning line that can be specifically used for image signals. Synonym useful line.

Available numbers are numbers that are available for assignment to subscriber access lines, or their equivalents, within a switching entity or point of interconnection and are not classified as assigned, intermediate, administrative, aging, or reserved. Available numbers is a residual category that can be calculated by subtracting a sum of numbers in the assigned, reserved, intermediate, aged, and administrative primary… (Read More →)

A state where a (bidirectional or unidirectional) service is usable.
Note: Each direction of a service is assumed to be in the available state unless a transition to the unavailable state is observed without a subsequent transition to the available state. In this standard the transitions between the available and unavailable states are: (a) transition to the unavailable state occurs… (Read More →)

From the point of view of a user, the time during which a functional unit can be used.
Note: From the point of view of operating and maintenance personnel, the available time is the same as the uptime, i.e., the time during which a functional unit is fully operational.

A current-multiplying phenomenon that occurs in a semiconductor photodiode that is reverse-biased just below its breakdown voltage.
Note: Under such a condition, photocurrent carriers, i.e., electrons, are swept across the junction with sufficient energy to ionize additional bonds, creating additional electron-hole pairs in a regenerative action. [After FAA]

A photodiode that operates with a reverse-bias voltage that causes the primary photocurrent to undergo amplification by cumulative multiplication of charge carriers.
Note: As the reverse-bias voltage increases toward the breakdown, hole-electron pairs are created by absorbed photons. An avalanche effect occurs when the hole-electron pairs acquire sufficient energy to create additional pairs when the incident photons collide with the… (Read More →)