Guides are portable computers with the facilities of domestic computers, and in fact led the field in widely available computer graphics of a high quality. They are small, thin devices, battery-powered and now days rechargeable via microwave induction. They are monolithic rectangular blocks 30 x 22.5 cm with built-in colour Flat CRT displays somewhat magnified using a lens covering the upper part of the device with a membrane keyboard in the lower half of the case. They are capable of high resolution colour graphics, sound, voice synthesis and data storage on ultra-Compact Discs, and also have a two-way UHF connection for accessing online services and communication with domestic computers. As well as portability, an important feature of the design is to make it tough enough to withstand quite harsh physical treatment, since as a portable device it is likely to be bashed about a bit.
The Guide is inspired by two sources. The earlier is Alan Kay's "Dynabook" concept, dating from 1968. This was a theoretical computer design with many of the features now present in the Guide, including the size, flat screen and keyboard and the long battery life. The later trigger to its development was 'The Hitch-Hikers' Guide To The Galaxy', whose title refers to a handheld electronic encyclopaedia covering the entire Galaxy. In the television series, the Guide was depicted as having high-resolution colour graphics of a standard unavailable on small computers at the time and a realistic voice synthesis unit.
After Acorn Computers' unsuccessful bid to provide the domestic computers to the GPO domestic telecommunications service in 1985, it became clear that they would be unable to compete with Sinclair in that market, since subscribers perceived the Ambassador II rental system as a "free" computer. They were saved when Douglas Adams approached them in confidence with the idea of manufacturing a real portable computer resembling the Guide, copying its on-screen appearance as closely as current technology allowed. In particular, Adams insisted on voice synthesis and a high resolution colour display. Acorn engineers worked closely with Adams on the project for three years. They were considerably hampered by his tendency to perfectionism and desire to add extra features, which constantly disrupted the design process. He also has a strong tendency to miss deadlines.
By 1988, Acorn were on the brink of bankruptcy. They took the drastic step of emptying their offices, disconnecting their telephone lines and locking Adams and the team of designers in the offices with the windows boarded up for a week. Adams also made the helpful move of investing most of the royalties from his work in the project. At the end of that period, Acorn and Adams emerged with a working design which they were able to release in time for the Christmas market internationally, built using a factory funded largely by Adams himself.
The Guide was an immediate success, but caused conflict with the BBC because Adams' TV series was then perceived as free advertising for the device and was cancelled in 1989. After some litigation, the BBC reached an arrangement with Adams that the Guide would be used as a resource in the government's computer literacy project. The BBC also opened a new "channel" which provided high-bandwidth information services specifically designed for the Guide later in the year. This was a UHF channel which constantly transmitted software and other information in a loop which at first only the Guide was able to receive. This service was later made available to the Sinclair Ambassador III shortly before it went into production in 1991.