![]() First eight-bit Heathkit H8 computer | |
Developer | Heathkit |
---|---|
Manufacturer | Heathkit |
Type | Microcomputer |
Release date | 1977 |
Operating system | CP/M, HDOS |
CPU | Intel 8080A |
Heathkit's H8 is an Intel 8080A-based microcomputer sold in kit form starting in 1977. The H8 is similar to the S-100 bus computers of the era, and like those machines is often used with the CP/M operating system on floppy disk.
The main difference between the H8 and S-100 machines is the bus; the H8 uses a 50-pin bus design that was smaller, more robust and better engineered electrically. The machine also includes a bootstrap ROM that makes it easier to start up, including code for running basic input/output and allowing input through a front-mounted octal keypad and front panel display, instead of the binary switches and lights used on machines like the Altair 8800.
The H8 requires a separate terminal to be truly useful; Heathkit introduced several terminals as well. A successor model, the "All-in-One" Heathkit H89, combines a Z80 processor board and a floppy disk drive into the cabinet of an Heathkit H19 terminal. This model also was sold in fully assembled form as the WH89. These were later sold by Zenith Electronics with their name on the front as the Zenith Z-89.
MITS announced the Altair 8800 in January 1975 and started selling kits soon after. Marketed to electronics hobbyists through trade magazines like Popular Electronics , the company founders felt there would be limited appeal and expected to sell only a few hundred systems. Instead, they received orders for thousands in the first month. Sales were so much greater than expected that MITS was unable to clear the order backlog for the better part of the year. [1]
The Altair sparked off such intense interest in the microcomputer world that a number of other companies jumped in to fill the sales backlog, building machines that were clones of the Altair. The primary component of this design is the S-100 bus, so named because it uses a 100-pin edge connector that MITS found at bargain prices when they were designing the machine. Unfortunately, the pins are connected from the backplane with a disorganized layout, and it has a number of problems that make it unreliable. [2]
Standardization led to a flourishing of companies selling into the S-100 market. The introduction of floppy disk controllers and the disk-based CP/M operating system dramatically improved the system's capabilities and started the process of turning them into practical small-business tools. By the late 1970s they were beginning to displace minicomputers and other systems in a number of roles.
Heathkit was a long-established player in the electronics market, making kits for products that had proven themselves in the market. Some of these were quite complex, including a color television. [3] The company had considered designing a kit computer as early as 1974, but concluded that it was not a good fit for their traditional market. The successful launch of the Altair changed things, and in 1977 decided to design a kit similar to the Altair but addressing its more obvious shortcomings. The H8 was announced in July 1977 and started selling that fall at a price of $379. [4] [5] [6]
For full functionality, the system also requires a 4 KiB SRAM card ($139) and some form of storage controller; at a minimum this would be the H10 paper tape punch/reader or the H8-5 Serial I/O card ($110) which controls a cassette tape, using a 1200-baud variant of the Kansas City standard format. [4] Another common accessory is the H9 video terminal, which is also driven by the H8-5 card; although any serial terminal will suffice. The H9 is limited to upper case characters and 12 display lines, and uses a cheap array of switches for its keyboard. It was eventually superseded by the H19 terminal, a more ergonomic design, and capable of lower-case and graphic-like characters. The H19 became a major product line of its own. The H17 floppy disk system became available in 1978, normally sold with one drive but expandable with a second (and later to three). Use of the H17 requires at least 16 KiB of RAM. The H8 can run CP/M, and often did, but early machines require either a special version of CP/M that was "org'd" at 8 KiB instead of zero, or a small hardware modification and an updated ROM to do so. Heath also offered HDOS, which was written by Gordon Letwin. Letwin later went to Microsoft and was chief architect of OS/2.
At the time the H8 was introduced, the computer market was in the midst of a shift from the hobby market that had spawned it to a "user" market that purchased pre-assembled machines. [4] Heath followed this trend and introduced the WH8 in fully assembled form for $475. [4] Like the H8, the WH8 requires several other cards for functionality. The disk drive system came fully assembled as the WH17. For the CP/M operating system, Heathkit provided the WH67, a 10 MB eight-inch hard drive and the H47 eight-inch floppy disk system.
In 1978 Heath introduced the Heathkit H88 which integrated the H19 terminal and a new Zilog Z80-based single-board processor into the case of the H19. A version with a disk drive incorporated to the right of the terminal screen became the H89. The machines bear a strong resemblance to the TRS-80 Model III and similar all-in-one computers. The H89 was sold both in kit form for $1595, and fully assembled form as the WH89 for $2295.
Soon after the introduction of the H89, Heathkit was purchased by Zenith, who were looking to enter the microcomputer market. [7] They continued sales of the H89 with their own labeling on the front as the Zenith Z89. Eventually, Zenith Data Systems (Heathkit plus the computer division of Zenith) was purchased by Bull HN (CII Bull, Honeywell and Nippon Electric) because they needed a US maker of microcomputers to comply with government purchase requirements. Kit sales were ended soon after that purchase. [8]
Heath chose not to implement the S-100 bus and instead created their own, known as "Benton Harbor Bus" after their home town. [4] The bus is based on a 50-pin connector and laid out to avoid the electrical problems of the S-100 system (like +5V and ground being placed beside each other). The H8 is packaged in a box-like chassis with pressboard sides and metal sheeting for the rest of the case. The top sheet is heavily perforated to form cooling vents.
The machine is built up from the backplane mounted on the right-hand side panel of the case, with ten 50-pin card slots. [9] The first and last slots are spaced differently from the rest, and the power supplies occupy some of the space needed for the last card. This means that the last card not only has to accommodate the narrow spacing but also cannot be full-length, leaving eight "standard" slots available for full-length cards. The front panel plugs into the first slot and the CPU plugs into the second, leaving seven for further expansion. The card slots are arranged on an angle, which allows the case to be reduced in height. Each card contains its own voltage regulators, using the Z-shaped mounting bracket as a heat-sink. (Power distribution on the backplane is unregulated +8V and +/-18V; the cards regulate these to their requirements, typically +5V and +/-12V.)
Another notable change is the replacement of the front-panel toggle switches and lights of a standard early-model S-100 system with a keypad and seven-segment LED display (early S-100 machines like the Altair or IMSAI 8080 contain no ROM and when they are started, the user "keys in" a program via the toggle switches to read a paper tape. Once this "loader" program is ready, a paper tape containing a more complete loader can be read in, allowing the user to load programs from cassette or floppy disk).
On the H8, all of this code is already pre-installed in a 1 KiB ROM in a monitor program known as "PAM8", occupying locations 0 through 3FF16 and the H17 disk I/O drivers used for booting, occupying a 2 KiB ROM occupying locations 180016 through 1FFF16 [10] The ROM contains code to control the keypad and display, [11] booting it directly into an operable state. Several versions of the PAM-8 ROM were sold as upgrades; at one point Heathkit switched to using 2 KiB ROMs, occupying through 7FF16 and subsequently to a 4 KiB ROM occupying through FFF16. The ROMs interfere with the operation of standard CP/M, which assumes it can write the memory near location 0, in particular the interrupt handler pointers.
PAM8 and portions of HDOS use an unusual address notation called "split octal" [12] [13] where 16-bit numbers are split into two 8-bit numbers printed in octal: the first location was "000.000" and the location after "000.377" was "001.000". In order to distinguish numbers in split-octal notation from 16-bit octal numbers, the two digit groups are often separated by a special symbol. Most mini- and micro-computers use either straight octal (377 was followed by 400) or hexadecimal.) With the introduction of the optional HA8-6 Z-80 processor replacement for the 8080 board, the front-panel keyboard got a new set of labels and hexadecimal notation replaced octal. [14]
The 50-pin "Benton Harbor Bus" was considered an improvement on the S-100 bus. [15] [16] The 50-pin bus of the H8 contains sixteen address lines, eight data lines, 5 interrupt lines, and the system control lines. Like the S-100 bus, it does not supply +5 V; each card is expected to have its own local +5 V regulator powered from "unregulated" +8 V on the bus. [17]
Heathkit also introduced their own dialect of the BASIC programming language. Two versions were available, Benton Harbor BASIC that supported the most basic commands and lacked string variables, and Extended Benton Harbor BASIC which required at least 24 kB of memory and added string variables, integer types, and commands for working directly with the floppy disk without having to exit to CP/M or the monitor. Modelled on Dartmouth BASIC, as opposed to popular later variations like HP Time-Shared BASIC or Microsoft BASIC, the language had a number of idiosyncrasies. [18]
The Aster CT-80 is a 1982 personal computer developed by the small Dutch company MCP, was sold in its first incarnation as a kit for hobbyists. Later it was sold ready to use. It consisted of several Eurocard PCB's with DIN 41612 connectors, and a backplane all based on a 19-inch rack configuration. It was the first commercially available Dutch personal/home computer. The Aster computer could use the software written for the popular Tandy TRS-80 computer while fixing many of the problems of that computer, but it could also run CP/M software, with a large amount of free memory Transient Program Area, (TPA) and a full 80×25 display, and it could be used as a Videotext terminal. Although the Aster was a clone of the TRS-80 Model I it was in fact more compatible with the TRS-80 Model III and ran all the software of these systems including games. It also had a built-in speaker which was compatible with such games software.
The Altair 8800 is a microcomputer designed in 1974 by MITS and based on the Intel 8080 CPU. Interest grew quickly after it was featured on the cover of the January 1975 issue of Popular Electronics and was sold by mail order through advertisements there, in Radio-Electronics, and in other hobbyist magazines. According to Harry Garland, the Altair 8800 was the product that catalyzed the microcomputer revolution of the 1970s. It was the first commercially successful personal computer. The computer bus designed for the Altair was to become a de facto standard in the form of the S-100 bus, and the first programming language for the machine was Microsoft's founding product, Altair BASIC.
The Kansas City standard (KCS), or Byte standard, is a data storage protocol for standard cassette tapes at 300 bits per second. It originated in a symposium sponsored by Byte magazine in November 1975 in Kansas City, Missouri to develop a standard for the storage of digital microcomputer data on inexpensive consumer quality cassettes. The first systems based on the standard appeared in 1976.
The IMSAI 8080 is an early microcomputer released in late 1975, based on the Intel 8080 and S-100 bus. It is a clone of its main competitor, the earlier MITS Altair 8800. The IMSAI is largely regarded as the first "clone" microcomputer. The IMSAI machine runs a highly modified version of the CP/M operating system called IMDOS. It was developed, manufactured and sold by IMS Associates, Inc.. In total, between 17,000 and 20,000 units were produced from 1975 to 1978.
Heathkit is the brand name of kits and other electronic products produced and marketed by the Heath Company. The products over the decades have included electronic test equipment, high fidelity home audio equipment, television receivers, amateur radio equipment, robots, electronic ignition conversion modules for early model cars with point style ignitions, and the influential Heath H-8, H-89, and H-11 hobbyist computers, which were sold in kit form for assembly by the purchaser.
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Processor Technology Corporation was a personal computer company founded in April 1975, by Gary Ingram and Bob Marsh in Berkeley, California. Their first product was a 4K byte RAM board that was compatible with the MITS Altair 8800 computer but more reliable than the MITS board. This was followed by a series of memory and I/O boards including a video display module.
The Z-89 is a personal computer introduced in 1979 by Heathkit, but produced primarily by Zenith Data Systems (ZDS) in the early 1980s. It combined an updated version of the Heathkit H8 microcomputer and H19 terminal in a new case that also provided room for a built-in floppy disk on the right side of the display. Based on the Zilog Z80 microprocessor it is capable of running CP/M as well as Heathkit's own HDOS.
The Sol-20 was the first fully assembled microcomputer with a built-in keyboard and television output, what would later be known as a home computer. The design was the integration of an Intel 8080-based motherboard, a VDM-1 graphics card, the 3P+S I/O card to drive a keyboard, and circuitry to connect to a cassette deck for program storage. Additional expansion was available via five S-100 bus slots inside the machine. It also included swappable ROMs that the manufacturer called 'personality modules', containing a rudimentary operating system.
George Morrow was part of the early microcomputer industry in the United States. Morrow promoted and improved the S-100 bus used in many early microcomputers. Called "one of the microcomputer industry's iconoclasts" by Richard Dalton in the Whole Earth Software Catalog, Morrow ran his own computer business, Thinker Toys, Inc., later Morrow Designs. He was also a member of the Homebrew Computer Club.
The Z-100 computer is a personal computer made by Zenith Data Systems (ZDS). It was a competitor to the IBM PC.
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North Star Computers Inc. was an American computer company based in Berkeley, California existing between June 1976 and 1989. Originally a mail order business for IMSAI computers, it soon developed into a major player in the early microcomputer market, becoming first known for their low-cost floppy disk system for S-100 bus machines, and later for their own S-100 bus computers running either the CP/M operating system or North Star's own proprietary operating system, NSDOS. North Star BASIC was a common dialect of the popular BASIC programming language. They later expanded their lineup with dual-CPU machines able to run MS-DOS, and a server version running either DOS or Novell NetWare.
PolyMorphic Systems was a manufacturer of microcomputer boards and systems based on the S-100 bus. Their products included the Poly-88 and the System 8813. The company was incorporated in California in 1976 as Interactive Products Corporation d/b/a PolyMorphic Systems. It was initially based in Goleta, then Santa Barbara, California.
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