The Sinclair ZX81 is a Personal computer 8 bits, conceived and marketed by the Sinclair Research in 1981. The case was black with a Clavier with membrane; the distinctive appearance of the machine came from the work of the industrial designer Rick Dickinson.

Successor of ZX80, this computer at reduced price, based on a Microprocesseur Zilog Z80 gave rhythm with 3,25 MHz had random access memory for the programs and posting. This one was done in black and white (22 lines of 32 characters) on a television set SECAM, without its but with a keyboard extra-dish and sensitive (Clavier with membrane).

The design of the ZX81 aimed to produce a computer with the performances certainly modest, but at a reasonable cost. That passed initially by a reduction of the number of the components and by the optimization of their use. In this respect one can note two interesting characteristics:

First of all the presence of a Integrated circuit dedicated, the ULA. Conceived specifically for the ZX81, it replaced 18 circuits standard TTL ZX80 of origin.

But the most astute remainder undoubtedly technique retained for the video control which was ensured by the microprocessor itself. Thus the frequency of 3,25 MHz was only justified to make it possible Z80 to be " compatible" with the line frequency of the television sets. The largest part of the machine time was devoted to trace the points of the matrices of characters on the screen. The code of the programs of the user was treated only at the time of the returns of line of the Cathode tube and during the sweeping of the empty zones in top and bottom of the screen.

A " mode; FAST" allowed nevertheless to discharge the microprocessor from video control. The screen of the television set then covered snow and the programs, accelerated considerably, could nothing any more post.

The programming was done in BASIC by typing the instructions which were printed on the keys of the keyboard. The BASIC made it possible to programme indirectly out of assembler language by the means of orders PEEK and POKE. The machine was proposed in kit to be gone up for 490 francs French in 1981.

Many peripherals were available, of which an extension of memory of, a thermal Imprimante and a keyboard with keys (calculator kind) which was stuck on the keyboard of origin. Software S, whose many plays were marketed. The safeguards of programs and data were possible on a Magnétophone with cassette S

Its price (unbeatable at the time), and especially its manual , which taught in a very teaching way the concepts of programming in BASIC, made a very great success of them, in spite of its poor performances, its BASIC incomplete, its grotesque graphic resolution and its lack of color. It was named the Initiator and made it possible many future data processing specialists to take their first steps with less expenses and without much risk.

The American version of the ZX81 was Timex/Sinclair 1000.

See too

• Cleaves Sinclair for more information.
• Planet Sinclair
• Applet Java emulator of ZX81

References