... IIRC one of the strange things with it was that it seemed to have a sound card. It's been many years since I've opened it. Perhaps some relationship to the cassette connector on the back ? Should I ever get thru my lengthy to-do list I'll spend some time on it. Nice to know there are now disk images available for it, and also the manual.
Lawrence
What you have is a cassette interface board, which was used for storing/retrieving data off of audio cassettes.
The H-88 was the computer shipped with just the cassette interface board, and anywhere from 16K to 48K of RAM.
The H/Z-89 was the computer shipped with an H-17 hard sectored disk controller card. The H/Z-90 (don't recall if the kit version used the -90 or not) would have included the H/Z-37 soft sectored controller board, which would work with single or double sided 40 or 96tpi drives. Somewhere in the mix was also a new set of relocating ROMs that moved the bootloader to high RAM so the OS could load at 0x0000; this was necessary for CP/M to run unmodified applications (which expected a jump table at 0x0000 and a program start at 0x0100).
As an aside, someone once published a hacked CP/M BIOS which allowed the hard sectored controller to run 96tpi drives, though finding compatible media was a bit of an adventure!
Heath also came out with the H/Z-47 8" controller, which could run 1 or 2 single or doublesided 8" floppies; there was also the H/Z-67 Winchester controller, which ran a dedicated subsystem containing an 8" floppy and an 8" hard drive.
A couple of other firms, Magnolia and CDR, also put out soft-sectored 5-1/4 controllers; the CDR card could also, if memory serves, control 8" drives.
There were also software and hardware hacks to get the H/Z-37 to work with 4MHz and 6MHz CPU upgrades, and to get the 37 to address 4 drives (it could only do 3 with a stock BIOS).
My favorite goody was the CDR RAMdisk card, which let you stuff a palatial 1MB of RAM in the machine and treat it as a 900KB RAMdisk; you could even hard reset the box and reboot off it! So long as the power didn't glitch (a big if in Florida!) that gizmo made the 89 the next best thing to instant in response.
Alas, my 89 CPU eventually succumbed to a lightning strike. The machine still lives on, however, with an Ampro LittleBoard+ and a 100MB SCSI hard drive. Gotta have that green screen to play Adventure!
http://www.afn.org/~scotsman/photos/h89.and.toaster.oven.jpg