The language became more widespread with the introduction of DEC's PDP-16 RT-Level Modules (RTMs) and a book describing their use.At least two implementations of the basic ISP language (ISPL and ISPS) followed.ISPS was well suited to describe relations between the inputs and the outputs of the design and was quickly adopted by commercial teams at DEC, and by several research teams in the US and among its allies in the North Atlantic Treaty Organization (NATO).

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