The ZX81 cuts away computer mystique. It takes you straight into BASIC, the most common, easy-to-use computer language. You simply take it out of its box, plug it in to your TV, switch it on at the mains—and start. With the manual in your hand, you'll be running programs in an hour. Within a week, you'll be writing complex programs of your own, with confidence and competence.
Sinclair's ZX81 was the successor to their popular ZX80 Personal Computer. While the hardware of both computers were nearly identical, the ZX81 included an NMI (non-maskable interrupt) generator, granting the ZX81 the ability to simultaneously execute program code and display a picture. This new SLOW mode significantly cut the effective CPU speed, but allowed the ZX81 to be a much more suitable game-playing device than its predecessor.
NEC P1X108-144 D780C-1 (Z80 compatible) @ 3.25MHz
|Resolution||32x24 characters (8x8 px characters) 256x192 px (HiRes video mode)|
|Palette||monochrome (normal and inverted)|
|Graphics||64 custom characters, defined in ROM|
|Input||Flat, pressure-sensitive membrane, QWERTY keyboard|
Timex Sinclair 1000
Perfectly Normal Site is an approachable introduction to ZX81 assembly language programming, offering "all the source, tools and info you need to write HiRes games on a real ZX81." The site has sections on ZX81 Hardware, Emulation, Development, and ZX81 HiRes, including lists of utilities, start templates, and code examples.
Thomas Harte's Clock Signal, or CLK, is "an an MIT-licensed open-source emulator of a collection of 8-bit computers and consoles for Linux, macOS and BSD."
chernandezba's ZEsarUX is "an open-source, multi-system emulator originally made for Unix systems and later adapted for other operating systems."