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H > HEATHKIT / ZENITH  > H-89   


The H-89 was sold under the two names: Heathkit H-89 and Zenith Data Systems Z-89. The H-89 was sold in kit form, the Z-89 came assembled.

It originally came with 16 KB of memory, later versions provided up to 48KB on the main CPU board (in groups of 1 KB chips). Zenith and Heathkit offered a 16 KB expansion card ($120) for a total of 64 KB when using CP/M.

The system was identical to the H-19 video terminal but had an additional CPU board between the CRT and the terminal board. (Really identical because Heath offered upgrade kits to convert an H-19 to an H-88/H-89 computer).

It used hard sectored disks with a built-in card controller. Under either H-DOS or CP/M, disk capacity was of 90 KB. Another model the H-88 was identical to the H-89, but did not include the floppy drive or controller. It had a cassette port.

A couple of years later, the H/Z-37 soft sectored controller and ROMS came out, then was replaced with a double 5.25" floppy disk drive called H/Z-87 (102 KB, 250 ms). A double 8" floppy disk drive called H/Z-47 (1 Mb each) and a hard disk called H/Z-67, it contained one 10MB 8" winchester drive and one 8" floppy drive (like the one in the H/Z-47).

It ran under HDOS or CP/M (the operating system used 16 KB of RAM).
HDOS was originally written for the H-8, it ran without modification on the '89. This was a single-user OS written by J. Gordon Letwin for Heath. It included a Basic interpreter and assembler.
For CP/M, H/Z wrote a custom BIOS in assembler that the new user could further customize for his specific hardware and assemble right on the machine.
A version of MP/M was also available for the system.

A lot of extension boards were available for this computer including 64 KB memory boards, hard-disk controller cards, 3-port serial I/O board, H19 terminal board, etc.
A third party small upgrade card was also offered which doubled the processor speed to 4 Mhz.

An assembler/debugger was given with the DOS. A paper tape reader was available as well. Microsoft has adapted its various programming languages (Basic, Fortran, Cobol) for this computer. Borland also offered a version of Turbo Pascal that worked great with the CP/M.

Dennis reports:
The base H-89 had no graphic modes, just 33 graphic characters. At least two different add-on boards were created that gave the H-89 bitmapped graphics capabilities, but I'm pretty sure they both required hardware modifications to tie them in to the terminal board - this was not a simple plug-in expansion card



I was very lucky to have a father working in computing in the 1960''s through now. In 1980 he purchased an H89 kit and allowed me to do the entire assembly and learn CP/M. I also messed around in BASIC and Turbo Pascal on it for the summer between my fifth and sixth grades. I had plenty of time on computers before it, but the assembly of the H89 really taught me how systems work. By winter my dad had written some software for a local franchise owner to better manage his operations and the H89 got a new home. I did get to see it in use a few times after. Not until I got an Amiga 1000 did another computer mean as much to me. I have built and assembled many systems of various scales over the years. This will always be my first.

Thursday 22nd March 2018
Jason H. Jester (Earth)

The H89, when compared with the TRS-80s by Radio Shack, could be considered the equivilant of a Model 3˝ or "Three and a half". In other words, it was about halfway in power and features between a Model 3 (1980) and a Model 4 (1983). It could go to 64K RAM and the Model 3 was limited to 48K, but the Model 4 had 64K and could go to 128K. The H89 used a 2 Mhz Z80 like the Model 3$ the Model 4 ran at 4 Mhz. (though the H89 could be upgraded to 4 Mhz, the Model 4 could upgrade to 6 Mhz). The H89 had a big 80x24 screen like the Model 4, but the characters were alot fuzzier on the screen. (the Model 3 was 64x16). The keyboard on the H89 had a much better feel than the Model 4, though. Both could run CP/M, but the Model 4 had its own large library of TRSDOS 6 programs and ran all Model 3 programs as well. There was a company that made a one megabyte RAM board, and it was easy to install because it went into the H89''s card cage. The Model 4 could be upgraded to one megabyte, but you had to do alot of soldering on the CPU board. The H89 RAM board could be used only as a RAMdisk$ the Model 4 board had drivers which permitted its RAM to be used as general-purpose expansion memory for TRSDOS applications through its standard @BANK supervisor call.

Monday 5th June 2017
Jeff Joseph (Norfolk, VA)

I assembled a H89 whilst Principal at an elementary school. Wrote a program to number-crunch attendance for the dreaded Quarterly Report. The Superintendent saw it, and bought a TRS 80 for his needs. Mine was the first. Also played the horse race game on it, and figured out how to rename the horses after the School Board members. Computers for teaching came rapidly after this beginning.

Tuesday 25th February 2014
James Starbird (Van Buren, Arkansas)


NAME  H-89
MANUFACTURER  Heathkit / Zenith
TYPE  Professional Computer
YEAR  1979
KEYBOARD  Full stroke keyboard with numeric keypad
CPU  Zilog Z80
SPEED  2.048 MHz
RAM  From 16 KB up to 64 KB
ROM  Custom bootup & monitor
TEXT MODES  80 chars. x 24 lines ( + one independant line)
GRAPHIC MODES  No graphics mode. 33 graphic characters
COLORS  Monochrome green phosphore display
SOUND  Beep - HUG magazine had a article on how to use one of the serial ports as a crude
I/O PORTS  RS232 (two, up to six), Centronics, IEEE 488
BUILT IN MEDIA  90 KB floppy drive
POWER SUPPLY  Built-in power supply unit
PRICE  $1,800 as kit in 1979 w/ 1 floppy drive

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