of the microprocessor starting in 1971. Early microcomputers such as the Altair 8800 had front-mounted switches and diagnostic lights (nicknamed "blinkenlights") to control and indicate internal system status, and were often sold in kit form to hobbyists. These kits would contain an empty printed circuit board which the buyer would fill with the integrated circuits, other individual electronic components, wires and connectors, and then hand-solder all the connections.
While two early home computers (Sinclair ZX80 and Acorn Atom) could be bought either in kit form or assembled, most home computers were only sold pre-assembled. They were enclosed in plastic or metal cases similar in appearance to typewriter or hi-fi equipment enclosures, which were more familiar and attractive to consumers than the industrial metal card-cage enclosures used by the Altair and similar computers. The keyboard - a feature lacking on the Altair - was usually built into the same case as the motherboard. Ports for plug-in peripheral devices such as a video display, cassette tape recorders, joysticks, and (later) disk drives were either built-in or available on expansion cards. Although the Apple II series had internal expansion slots, most other home computer models' expansion arrangements were through externally accessible 'expansion ports' that also served as a place to plug in cartridge-based games. Usually the manufacturer would sell peripheral devices designed to be compatible with their computers as extra cost accessories. Peripherals and software were not often interchangeable between different brands of home computer, or even between successive models of the same brand.
To save the cost of a dedicated monitor, the home computer would often connect through an RF modulator to the family TV set, which served as both video display and sound system.
By 1982, an estimated 621,000 home computers were in American households, at an average sales price of US$530 (equivalent to $1,376in 2018). After the success of the Radio Shack TRS-80, the Commodore PET and the Apple II in 1977, almost every manufacturer of consumer electronics rushed to introduce a home computer. Large numbers of new machines of all types began to appear during the late 1970s and early 1980s. Mattel, Coleco, Texas Instruments and Timex, none of which had any previous connection to the computer industry, all had short-lived home computer lines in the early 1980s. Some home computers were more successful – the BBC Micro, Sinclair ZX Spectrum, Atari 800XL and Commodore 64, sold many units over several years and attracted third-party software development.
Almost universally, home computers had a BASIC interpreter combined with a line editor in permanent read-only memory which one could use to type in BASIC programs and execute them immediately or save them to tape or disk. In direct mode, the BASIC interpreter was also used as the user interface, and given tasks such as loading, saving, managing, and running files.One exception was the Jupiter Ace, which had a Forth interpreter instead of BASIC. A built-in programming language was seen as a requirement for any computer of the era, and was the main feature setting home computers apart from video game consoles.
Still, home computers competed in the same market as the consoles. A home computer was often seen as simply as a higher end purchase than a console, adding abilities and productivity potential to what would still be mainly a gaming device. A common marketing tactic was to show a computer system and console playing games side by side, then emphasizing the computer's greater ability by showing it running user-created programs, education software, word processing, spreadsheet and other applications while the game console showed a blank screen or continued playing the same repetitive game. Another capability home computers had that game consoles of the time lacked was the ability to access remote services over telephone lines by adding a serial port interface, a modem, and communication software. Though it could be costly, it permit