Xerox 820

The Xerox 820 Information Processor is an 8-bit desktop computer sold by Xerox in the early 1980s. The computer runs under the CP/M operating system and uses floppy disk drives for mass storage. The microprocessor board is a licensed variant of the Big Board computer.

Xerox introduced the 820 in June 1981 for $2,995 with two 5+1⁄4-inch single-density disk drives with 81K of capacity per diskette, or $3,795 with two 8-inch drives with 241K capacity. To beat the IBM PC to market, Xerox created little of the computer's design; it is based on the Ferguson Big Board computer kit and other off-the-shelf components, including a Zilog Z80 processor clocked at 2.5 MHz, and 64 KB of RAM.

Xerox chose CP/M as its operating system because of the large software library—The 820 is compatible with all Big Board software—and sold a customized version of WordStar for $495, although by 1982 the company offered the standard version for the same price.

By 1984, surplus 820 mainboards were available from Xerox for about $50 each, and one of these could be combined with other surplus components to build a working system for a few hundred dollars.

The Xerox 820-II followed in 1982, featuring a Z80A processor clocked at 4.0 MHz. Pricing started at US$3,000 (equivalent to $10,000 in 2025).

Hardware: The processor board is located inside the CRT unit, and includes the Z80A, 64 KB of RAM and a boot ROM which enables booting from any of the supported external drives in 8-bit mode.

Screen: The display is a 24-line, 80-character (7×10 dot matrix) white-on-black monochrome CRT, with software-selectable variations such as reverse video, blinking, low-intensity (equivalent to grey text), and 4×4-resolution graphics.

Communication ports: These include two 25-pin RS-232 serial ports (including one intended for a Xerox 620 or 630 printer or compatible, and one intended for a modem), and two optional parallel ports which can be added via an internal pin header, usable with a Xerox or other cable.