Xerox 820
 Xerox 820 |
|
| Manufacturer | Xerox |
|---|---|
| Release date | 1981 |
| Discontinued | 1985 |
| Media | 96kb 5¼-inch floppy disks, 300kb 8-inch floppy disks |
| Operating system | CP/M 2.2 |
| CPU | Zilog Z80A clocked at 2.5MHz |
| Memory | 64kB RAM, 4kb to 8kb ROM |
| Input | Keyboard |
| Dimensions | 32.8 x 38.1 x 34.3cm |
| Weight | 13.6kg |
The Xerox 820 was an 8-bit desktop computer sold by Xerox in the early 1980s. The computer ran under the CP/M operating system and used floppy disk drives for mass storage. The microprocessor board was a licensed variant of the Big Board computer.
Contents |
The original 820 [edit]
The original Xerox 820 used a Zilog Z80 processor clocked at 2.5 MHz, and had 64 kiB of RAM.
The 820-II [edit]
Overview [edit]
The Xerox 820-II followed in 1982, featuring a Z80A processor clocked at 4.0 MHz. Pricing started at $3000.[1]
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 display was a 24-line, 80-character (7x10 dot matrix) white-on-black monochrome CRT, with software-selectable variations such as reverse video, blinking, low-intensity (equivalent to grey text), and 4x4-resolution graphics.[1]
Communication ports These included two 25-pin RS-232 serial ports (including one intended for a Xerox 620 or 630 printer or compatible), and two optional parallel ports which could be added via an internal pin header, usable with a Xerox-supplied or other cable.
Keyboard: A bulky 96-character ASCII keyboard with a 10-key numeric keypad and a cursor diamond which otherwise defaulted to Ctrl-A to Ctrl-D. It also included "Help" and "Line Feed" keys, and was attached to the back of the CRT unit by a thick cable.[1]
Software: A typical 820-II came with the CP/M 2.2 operating system, a diagnostic disk, a copy of WordStar word processor software, and Microsoft's BASIC-80 computer language.
Disk storage [edit]
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 be daisy-chained via a port on the back.
| Component | Capacity | Tracks/disk | Sectors/track | Bytes/sector | Notes |
|---|---|---|---|---|---|
| Dual 5.25" single-sided floppy drives | 81K usable single density, 155K double density | 40 | 18 or 17 | 128 or 256 | All floppy disks are soft-sectored |
| Dual 5.25" double-sided floppy drives | 172K usable SD, 322K DD | 80 | 18 or 17 | 128 or 256 | |
| Dual 8" single-sided floppy drives | 241K usable SD, 482K DD | 77 | 26 | 128 or 256 | |
| Dual 8" double-sided floppy drives | 490K usable SD, 980K DD | 154 | 26 | 128 or 256 | |
| 8" rigid disk drive | 8.19MB | 1024 | 32 | 256 | Provided with an 8" double-sided floppy drive |
Reference: 820-II Operation Manual[1]
The Basic Operating System (BOS) monitor [edit]
The system could function to a limited extent 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, perform disk operations, take keyboard input, write to the display, et al.
Reference: 820-II Reference Guide[2]
Model 16/8 [edit]
An updated version of this computer called the model 16/8 ran dual CPUs, an 8-bit Z80 and 16-bit Intel 8086, which could be booted jointly or separately. The operating system was 8-bit CP/M 80 and 16-bit CP/M 86, and it was supplied with the Word Perfect word processor and dBase II database management system. It had double 8" floppy disk drives, a 12" monochrome monitor and a daisywheel printer. Later in 1984 double 5.25 floppy disk drives, a portrait-size blue monitor, and a laser printer were offered. The Model 16/8 is also called a Xerox 823
