- Xerox 820
The Xerox 820 was an
8-bit desktopcomputer sold byXerox . The computer featuredfloppy disk drives for mass storage, and used theCP/M operating system. The design of the microprocessor board was a licensed variant of theBigboard computer.The original 820
The original Xerox 820 used a
Zilog Z80 processor clocked at 2.5 MHz, and boasted 64kiB ofRAM .The 820-II
Overview
The Xerox 820-II followed in 1982, featuring a Z80A processor clocked at 4.0 MHz. The units were priced starting at $3000.Xerox 820-II Personal Computer Operation Manual, 1982.]
Hardware: The processor board was located inside the CRT unit, and included the Z80A, 64K of RAM (with optional expansion up to 32-34K), and 6-8K of ROM (expandable).
Screen: The CRT itself was a 24-line, 80-character (7x10 dot matrix) white-on-black monochrome display, with software-selectable variations such as
reverse video , blinking, low-intensity (equivalent to grey text), and 4x4-resolution graphics.Communication ports These included two
RS-232 25-pin serial ports (including one intended for aXerox 620 or 630 printer or compatible) and two optional parallel ports which could be added via an internal pin header with either an official Xerox cable or one's own modification.Keyboard: The keyboard was a bulky 96-character ASCII with a 10-key numeric keypad and a cursor diamond which otherwise defaulted to control characters ^A-D. It also included "Help" and "Line Feed" keys, and attached to the back of the CRT unit with a thick cable.
Software: An example 820-II would come with a copy of
CP/M 2.2, a diagnostic disk, a copy ofMicroPro 'sWordStar suite, andMicrosoft 's BASIC-80.Disk storage
Although it may be confusing to users of modern computers, the CRT unit contained the processor, and a large port on the back connected via heavy cable to a disk drive, allowing a wide variety of configurations. Disk drives could even be daisy-chained to each other via a port on the back of a unit.
Reference: 820-II Operation Manual
The Basic Operating System (BOS) monitor
The system could also function in a limited fashion without having to load a
disk operating system . The system monitor in ROM allowed, at boot-up, a variety of uses via one-letter commands followed by attributes.A user would normally use the "(L)oad" command to load a bootstrap loader (i.e., for CP/M) from a floppy or the fixed disk. One could also access a "(T)ypewriter" mode for direct interface with the serial printer port and basic typing on screen. "(H)ost terminal" would allow the 820-II to interface as a terminal via either of the serial ports, as specified, at up to 19.2 kbit/s.
For low-end system operations, however, a user could manually read or write to memory, execute code at a particular location in memory, read from or write to the system ports, or even read a sector from a disk. Further, (documented) calls to BOS subroutines allowed a skilled user or program to restart the system, perorm disk operations, take keyboard input, write to the display, et al.
Reference: 820-II Reference Guide [Xerox 820-II Personal Computer CP/M 2.2 Operating System Reference Guide, 1982.]
Model 8/16
An updated version of this computer called the model 8/16 ran dual CPUs, Z80 and
Intel 8086, which could be booted jointly or separately. The software for it wasCP/M 80 and CP/M 86, plusWordperfect and Dbase II. It featured a double 8" floppy disk drives, a 12" b/w monitor and aDaisywheel printer . Later in 1984 double 5.25 floppy disk drives, a portrait size blue monitor, and a laser printer were offered.Notes
External links
* [http://www.old-computers.com/museum/computer.asp?st=1&c=15 820 picture and specifications]
* [http://www.old-computers.com/museum/computer.asp?st=1&c=487 820-II picture and specs]
* [http://www.old-computers.com/museum/computer.asp?st=1&c=14 8/16 picture and specs]
* [http://mccworkshop.com/computers/comphistory7.htm Article about the 820-II with a rigid drive option From mccworkshop.com.]
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