When the modus operandi of a new product or process is fundamentally different from its predecessor, then obsolescence will not be far away. This obsolescence may also include a loss of process machinery, materials processing methods and application knowledge - once gone, it may never return. The speed at which the obsolescence occurs is, in part, due to the depth of the paradigm shift the new technology engenders. This transitional change may happen quickly - such as the fairly rapid death of the slide rule once the low-cost basic pocket calculator was introduced c.1972 - or more slowly (such as in the case of the reciprocating steam engine or mechanical television).

As the march of the progress of technological development is ever onwards and forwards, it is, perhaps, worthwhile to reflect on those devices, processes, materials and finished articles that have fallen by the wayside. Such finished goods utilizing these anachronistic technologies are now attractive to collectors as they hearken to a simpler age.

But what devices perished so rapidly that they are in danger of becoming forgotten It is worth noting a few examples, such as:

*Wire recording - largely replaced by magnetic tape c.1951 except in certain specialist applications. *8-track tape - replaced by the compact cassette and other media c.1970. However, the 8-track cartridge may still be found in radio stations as a jingle playback device. *Slide rules - replaced by pocket calculators from the late 1960 s onwards. It is worth noting that, allegedly, Wernher von Braun designed the Saturn V rocket using a slide rule for the computation. *Mechanical television - the Paul Gottlieb Nipkow development of the scanning disc was brought to practical fruition by John Logie Baird in the late 1920 s. The system was replaced c.1936 by the all electronic television work of Philo Farnsworth and Vladimir Zworykin *Electro-mechanical s) replaced by all-electronic equivalents from 1960 onwards *Cold cathode tube displays (such as the Nixie tube) - replaced by LED and LCD displays from c.1970. *Vacuum tubes themselves have largely been replaced by single transistors or (more usually) integrated circuits. They remain, however, in production for high fidelity audio use and in specialist applications such as radar, TV & radio transmitters, x-ray and microwave applications and as the cathode ray tube. *Airships for trans-continental passenger services replaced by better aircraft c.1936 (especially after the failures of the R101 and Hindenburg disaster) *Electro-mechanical switching in a telephone exchange - replaced by electronic and digital connection systems. *steam engine for industrial machine use - industrial process machines are now powered by self-contained drive systems rather than from a central plant. *Certain radio navigation systems for commercial use - such as LORAN and the Decca Navigator. Now replaced by cheap and highly accurate Global Positioning System devices.