ZX81

The ZX81 is a home computer produced by Sinclair Research and manufactured in Scotland by Timex Corporation. It was launched in the United Kingdom in March 1981 as the successor to Sinclair's ZX80 and was designed to be a low-cost introduction to home computing for the general public. It was hugely successful and more than 1.5 million units were sold before it was eventually discontinued. The ZX81 found commercial success in many other countries, notably the United States, where it was initially sold as the ZX-81. Timex manufactured and distributed it under licence and enjoyed a substantial but brief boom in sales. Timex later produced its own versions of the ZX81 for the US market – the Timex Sinclair 1000 and Timex Sinclair 1500. Unauthorised clones of the ZX81 were produced in a number of countries.

The ZX81 was designed to be small, simple, and above all cheap, using as few components as possible to keep the cost down. Video output was to a television set rather than a dedicated monitor. Programs and data were loaded and saved onto audio tape cassettes. It had only four silicon chips on board and a mere 1 KB of memory. The machine had no power switch or any moving parts (with the exception of a VHF TV channel selector switch present on early "ZX81 USA" models and the Timex-Sinclair 1000), and used a pressure-sensitive membrane keyboard for manual input. The ZX81's limitations prompted the emergence of a flourishing market in third-party peripherals to improve its capabilities. Such limitations, however, achieved Sinclair's objective of keeping the cost of the machine as low as possible. Its distinctive design brought its designer, Rick Dickinson, a Design Council award.

Polychlorinated dibenzodioxins

Polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of polyhalogenated organic compounds that are significant environmental pollutants.

They are commonly but inaccurately referred to as dioxins for simplicity, because every PCDD molecule contains a dibenzo-1,4-dioxin skeletal structure, with 1,4-dioxin as the central ring. Members of the PCDD family bioaccumulate in humans and wildlife because of their lipophilic properties, and may cause developmental disturbances and cancer.

Dioxins occur as by-products in the manufacture of some organochlorides, in the incineration of chlorine-containing substances such as polyvinyl chloride (PVC), in the chlorine bleaching of paper, and from natural sources such as volcanoes and forest fires. There have been many incidents of dioxin pollution resulting from industrial emissions and accidents; the earliest such incidents were in the mid 19th century during the Industrial Revolution.

The word "dioxins" may also refer to other similarly acting chlorinated compounds (see Dioxins and dioxin-like compounds).