HEATH/ZEINTH Z 80
The Heath/Zeinth Z 80
the King of Kits
For many years, the Heath Company, of
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
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!"
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
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
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
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
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
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