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The Heath/Zeinth Z 80

Heath the King of Kits

For many years, the Heath Company, of Benton Harbor , Michigan , sold kits for radio and audio test equipment and all kinds of electronic devices. Their expertise in this field was completely unchallenged. The thousands of catalogs they sent out brought electronics into every remote part of the United States . Heathkit designs were made simple and broken down into small steps so that failure was almost impossible as long as the builder followed the instruction book step-by-step to completion. They also had some retail stores in major markets where builders could get help with their projects. However, when the microcomputer revolution started in 1975, Heath was very slow to join in. They were selling microprocessor training kits when the new computer companies were selling computers.

The computer companies did not bother to write detailed instruction books and test them for accuracy. Their instructions would read, "Solder in all the resistors after checking the schematic for the correct values. Next, solder in all the capacitors." or "Be careful not to make solder bridges."

The first time I assembled an Imsai kit, I used the photograph in the advertisement to find out how the chassis went together. They never gave us a mechanical drawing of the assembly with the first ten kits I sold.

I remember listening to one of my salesman asking the customer, "You sure you know how to solder this? It sure isn't a Heathkit!"

 When Heath finally came up with kits worthy to be called Heathkit, they were strange machines compared with the industry standards. They did not use any of the standard programs and were a breed unto themselves.

The H8 was the first 8080 computer made by Heath. It had a sloping front panel mounting a 9-digit keypad which could be used to program it in machine language. However, it used octal notation rather than the Hex notation which was used on the S-100 machines. It was a bus machine with a unique 50-pin bus. Expansion cards and peripherals were available for the machine, including the memory and speech cards, the H7 floppy disk assembly, and the H10 paper tape reader/punch. The H8 needed at least 16K of memory for nominal operation and 48K if a floppy disk was to be used. The maximum memory capacity was 64K. The H8 had no internal video but was designed to be used with a terminal such as the H9 Video Terminal which had a 12" CRT.

Heath started with their own operating system, HDOS for disk operation, but added CP/M capability to give their users the ability to use all the software coming on the market for what was becoming the industry standard.

The basic H8 kit sold for only $350, but there was almost nothing you could do with the basic kit. You had to add memory boards and I/O boards and a terminal and disk system to really use the H8.

The Heath Company made a deal with Digital Equipment Corporation to incorporate the DEC LSI-11 CPU into a machine called the H11 which can be thought of as the first 16-bit micro. The resulting computer was supposed to be able to run PDP-11 software, but it was extremely limited because of its puny memory. The H11 was a disappointing effort for the customers, who thought they were getting a cheap DEC PDP-11.

The Heath Company started to fall on bad times at the start of the 1980s. The chip revolution had changed the entire electronics business, and people no longer built electronic kits because entire portions of the equipment were built into a single chip. The flood of imports had lowered the prices of radio, audio, video, and test equipment to levels where the kits cost more than completed units. However, Heath still had its value as a maker of educational and training equipment and texts. The company was bought out by Zenith Radio Corporation, who brought out completely new lines of computers.

The Heath/Zenith H-89 was the first of these machines and by far the most popular of the brand. It was sold as the Z-89 in its factory-built version, or H-89 as a Heathkit. The Z/H-89 was a desktop-integrated computer with a full keyboard and a 12" non-glare CRT. Next to the CRT was a single 5 1/4" floppy disk drive. The double-density version of the disk controller could store 160K, and there was also a optional external floppy disk and a hard disk option which could store 11 Mbytes. The standard unit came with 48K of RAM, and it could be expanded to 64K. An unusual feature of the H-89 was the fact that it used two Z-80 CPU chips. One ran the computer while the other ran the video terminal functions.

The H/Z-89 was able to run the standard CP/M operating system and all the software available under that system. It quickly achieved a reputation as a solid workhorse of a computer, and had a large and loyal user community.

The H-89 kit was either $1,895 for a white CRT, or $1,995 for a green CRT. Assembled units were $2,895 for either a built-in disk drive, or a double-density controller for a double-density drive and a hard disk. The factory-built version was $3895.

The engineers at Zenith had an answer to the IBM PC, which was quickly obsoleting the Z-80 computers. It was their Z-100 Series which was also sold as a kit under the Heathkit "H" designation. The series consisted of the Z120 which was an all-in-one business computer with a 12" CRT. The Z-110 was a "flat-top" computer designed with high resolution graphics to mount an RGB color monitor.

The Z-100 series had two microprocessors. One was an 8088 designed to run under MS-DOS and the same 16-bit software as the IBM PC. The other CPU was an 8-bit 8085 which could run CP/M and all the thousands of programs available under that system. All the Heath computers had used their own bus system, but the S-100 departed from that and used a standard S-100 bus! Floppy disk storage was 320K per disk, and a 5MByte hard disk was available.

The Z-100 started out like a house-on-fire; it was an excellent computer, and it had the best color graphics of any machine on the market in those days. The problem was in the incompatible MS-DOS software. The special versions for the Z-100 were not kept current and the S-100 Bus made it incompatible with developments in expansion boards by third parties.

The Z-100 was replaced by MS-DOS-compatible machines from Zenith.

Zenith itself was bought out by Bull Group of France, who closed down the Heath

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