Tight coupling

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Not to be confused with the related concept in software architecture, tight coupling between two components of a distributed system, means that they are so closely interconnected or interrelated that the failure of one quickly or inevitably triggers failure of the other so that it is not practicable to shut the system down, isolate the failing component or otherwise reconfigure the wider system to operate safely before the failing components precipitate a catastrophic, system-wide failure.

Originates from Charles Perrow’s Normal Accidents.

Tightly coupled systems include Dams, power grids, nuclear power stations, aeroplanes and DNA.

Loosely coupled systems include post offices, universities, research and development and most manufacturing.

Features of tight and loose coupling

Tight coupling Loose coupling

Production delays not possible
Difficult to stop the component operating
Mandatory sequence of operation
No scope for changing sequence on the fly
Few buffers or redundancy in the system
Existing buffers are hard-wired and inflexible
Little scope for improvisation

Processing delays possible
Production sequence can be changed
Redundancy and slack on resources and personnel
Fortuitous buffers and redundancies in the system
Scope for improvision and substitution

See also