The Sinclair ZX81 was an 8-bit personal computer, designed by Sinclair Research and released by Timex Corporation in March 1981. The case was black with a membrane keyboard; the machine's distinctive appearance came from the work of industrial designer Rick Dickinson.
The successor to the ZX80, this low-cost computer, based on a Zilog Z80A microprocessor clocked at 3.25 MHz, had 1 KB of RAM for programs and display. The display was in black and white (24 lines of 32 characters) on a standard television set. The computer did not have a sound output
The design of the ZX81 was aimed at producing a computer with modest performance, but at a reasonable cost. This was achieved by reducing the number of components and optimizing their use. In this respect, two remarkable characteristics can be noted:
Half of the machine time (49.92%: 192×2×52 µs / (625×64 µs)) was spent drawing the dots of the character matrices on the screen. The user's program code was only processed during the CRT line feeds and during the scanning of the empty areas at the top and bottom of the screen.
However, the FAST command was able to offload the microprocessor from video control. The TV screen would then be covered with snow until a SLOW command reactivated the display. Operations were then performed twice as fast. There was nothing to prevent PRINT or PLOT during FAST mode, but the final result was not displayed until the display returned to SLOW mode.
Programming was done in Sinclair BASIC by typing the instructions that were printed on the keys of the keyboard. The BASIC offered the possibility to program indirectly in machine language by means of the PEEK and POKE commands. The machine was offered in kit form for 490 FF in 1981.
Many peripherals were available, including a 16 kB memory extension, a compact thermal printer and a keypad that could be glued on the original keyboard. Software, including many games, was marketed (Flight Simulator, Cobalt Simulator, Mazzog). Programs and data could be saved on a cassette recorder.
Its price (unbeatable at the time without the extensions), and especially its manual, which taught in a very pedagogical way the notions of programming in BASIC, made it a great success, despite its poor performance, its incomplete BASIC, its low semi-graphical resolution (but accessible in BASIC) and its lack of color. It was named "The Initiator" and allowed many future computer scientists to take their first steps at low cost and without much risk.
The American version of the ZX81 was the Timex Sinclair 1000, whose fundamental difference from the ZX81 was that it had 2k of RAM.