The Sinclair ZX80 was released by Science of Cambridge Ltd (later to be renamed Sinclair Research Ltd) in 1980.
Designed by Jim Westwood, the aim was to produce a commercial computer (as opposed to a purely hobbyist device like Sinclair's earlier MK14) from off-the-shelf parts as cheaply as possible. An example of this cost-cutting was the decision not to use a traditional moving-key keyboard. Instead a membrane keyboard of the type used on industrial machinery or white goods was used.
The ZX80 was available in either kit form for £69.95, or fully assembled for £99.95. It was the first assembled home computer to be marketed in the UK at under £100. (However a power supply was not included - the official Sinclair version would set you back a further £8.95.) Slight variants from the original UK version were created for international markets, but the changes were limited to dealing with alternative TV systems.
The computer was based around a Zilog Z80 CPU running at 3.5 MHz (though most ZX80s actually shipped with an NEC clone of the Z80). 1Kb of RAM was included as standard, though this could be expanded with external RAM packs. Sinclair offered a RAM pack which could support 1, 2 or 3 Kb of additional RAM. Later RAM packs became available which expanded the total capacity up to 16Kb.
Another example of the cost-cutting was that the expansion port to which RAM packs and other peripherals was connected was not a moulded connector, but merely an edge connector on an exposed section of motherboard. This could cause problems if the computer was knocked, resulting in the RAM pack being dislodged and work being lost. The same design, and the same problems carried on through later generations of Sinclair computers.
Unlike later Sinclair computers, the case was white. The need for a 'hump' on the top of the case covering the RF modulator and heat sink resulted in the computer being affectionately referred to as the "block of cheese".
The ZX80 was designed to be connected to a standard television, rather than an expensive dedicated monitor and included an RF out. Graphics were black and white only, with a screen resolution of 32 characters by 22 characters. Each character was an 8x8 pixel block. Graphics characters such as ▌or ▄ were available which allowed primitive graphics to be drawn. The ZX80 had no sound output.
The operating system and BASIC software was included on a 4Kb ROM. BASIC commands were not typed in full, rather pressing a key when a keyword was expected caused an entire keyword to appear. For example, pressing "I" would cause "INPUT" to appear. The keywords in a BASIC program were stored in memory as a single character, resulting in a significant reduction in memory storage required.
A significant limitation of the ZX80 for gaming was that it did not have dedicated display hardware. Dealing with the display had to be done in software. As a result the display could only be shown when the computer was waiting for user input. While processing, the screen went blank. This limitation was later overcome by Ron Bissell, who created a machine code routine which allowed the processing to be split up such that it ran in the time between refreshes of the TV display. This was released in 1981 as "Amazing Active Display" and allowed programmers to release games with (relatively) smooth animation.
Data storage was by connecting a standard domestic cassette tape recorder to connectors on the back of the ZX80. This also allowed for relatively cheap distribution of early commercial software, including games.
The ZX80 was superseded just 1 year later by the Sinclair ZX81, which had very similar hardware. The main difference was that the ROM was upgraded to 8Kb with additional capabilities, such as the ability to deal with floating point arithmetic. Also display hardware was included which allowed for smooth screen updates without the need for software routines such as "Amazing Active Display". When the ZX81 was released, Sinclair offered an upgrade kit consisting of the new 8Kb ROM and a replacement keyboard overlay with the new BASIC commands. This solder-less upgrade essentially turned the ZX80 into a ZX81, but without the new display hardware. Later third party modifications offered display hardware updates to turn a ZX80 with the 8Kb ROM into a fully-fledged ZX81, though these involved soldering additional hardware to the motherboard.