The operational advantages of IDM's recorded presets were hampered by the cumbersome procedure required to re-record a modified lighting state. A system which addressed this problem whilst retaining immediate access to any channel was the push button version of IDM (the /R for Rocker switch) which became the conceptual prototype for the first software computer lighting control. The DDM (Digital Dimmer Memory) was developed for the Royal Shakespeare Theatre, Stratford-upon-Avon, but immediately became recognised as the major world-class memory lighting control.

Based on software for a standard mini-computer which allows any degree of sophistication to be programmed in, or indeed re-programmed if future artistic styles demand different facilities from the lighting control. A system such as Rank Strand's DDM although capable of being operated simply is offered on the assumption that lighting will become more and more sophisticated and that the operator will ultimately use every facility to the full. Fade within fade facilities, instant modification of the intensity level of any control channel without the need to match the existing level, and a magnetic tape repertoire store in addition to the instant access ferrite-core store are all standard features of DDM.