The Sinclair ZX8I is a part of the UK-based Sinclair ZX Spectrum family and was the successor to the ZX80. Sinclair Research Ltd is a consumer electronics company founded by Sir Clive Sinclair in Cambridge, England.

Launched in March 1981, the ZX81 was based on the Zilog Z80 CPU and came with a one new chip, replacing the 18 chips in the ZX80. The machine cost £69.95 or, if you wanted to assemble it yourself, £49.95 in kit form. Sinclair also offered an add-on ROM to convert the ZX80 to the ZX81.

The ZX81 came in a sturdy black case and with various features, including a TV jack that let users plug it in to their color TVs, producing black characters on a green background.

Sinclair also offered a small printer to work with the ZX81 later in the 1981. The ZX Printer very compact, using a special metalized paper, and would print 32 characters to a line and nine lines to the inch. Users would plug it into the back of the computer using a stackable socket. The print was clear and readable.

The model in MuMoH has a memory pack with a whopping 16K RAM that can be plugged in the back to give users more memory.

The computer sold well in the UK as well as in the U.S. – mostly by mail order. Eventually Timex was granted a license to sell it in 1982, opening the door for even more users.

The ZX81 had originally been produced as learning machines for the person wanting to find out about computer programming, such as BASIC.

It can be noted, though, that the Sinclair might have been responsible for the industry we know today. Sinclair produced a whole new industry that included vendors offering software, user’s clubs, peripherals and even its own publication.

During the mid-1980s, the company Micronet800 launched a service allowing users to connect their ZX Spectrums via a Prism Micro Products modem to a bulletin board system known as Micronet hosted by Prestel. Though very similar to the Internet, the service was proprietary and fee-based.

References:
http://www.sincuser.f9.co.uk/046/sstory.htm
http://en.wikipedia.org/wiki/Sinclair_Research