Shelton Advert - April 1981

This is the first known advert for Chris Shelton's Sig/Net, the range of hardware which is considered as perhaps the first ever modular multi-user personal computer system^[1].

With its budget monochrome design with a single spot colour, the advert came from Shelton Instruments of Copenhagen Street in London, a company founded in the early 1970s.

By the time of the advert, Chris Shelton was already well-known as the designer of the Nascom 1, as well as for his earlier work with microcontrollers and microprocessors.

The more conventional arrangement for multiple users at the time was to share a central micro - including its CPU, memory and disks - via a number of serial ports, each connected to a terminal.

As more users were added, performance generally got worse as all users were sharing everything.

With Sig/Net, this idea was modified so that users had their own CPU and RAM "module", but the modules were all connected over a flexible 26-way "port bus" to a base module with hard-disk storage, printers, and so on.

There was a downside to this arrangement - these interconnect cables could only be up to a metre long, however each satellite supported up to three connected terminals, and these could run over RS-232 at much longer distances.

The components of the satellite units were also modular, however a basic set up - CPU and RAM, a floppy disk controller, twin serial connections and two power supplies, one for the CPU and one for the floppies - retailed for £1,299, which is about £6,970 in 2026.

However that didn't include the cost of the terminals or - apparently - the actual floppy disk drives.