What is a Heathkit H120?

The H-120 was a generic designation for the "all-in-one" version of the Heathkit / Zenith Data Systems Z-100 series of personal computers (actual units had a slightly different model number depending on their configuration). It was a dual processor system, 8085 and 8088, could run both CP/M and MS-DOS (but it was not PC compatible at the hardware level). It had a large motherboard that included a 5-slot S-100 expansion backplane at the rear. The system was available both in kit form and assembled, the assembled models carried Zenith Data Systems rather than Heathkit labels but were identical. The kit was mostly pre-assembled, only the floppy disk controller and video monitor deflection boards were actually build by the buyer, otherwise the kit was just a final assembly task of factory assembled & tested boards. The system had a floppy disk controller that could support both 8" and 5" drives simultaneously (I think four 8" and three 5" drives). A hard drive controller was also offered that could support two MFM hard drives. Video came from a dedicated video board that was, for it's time, quite sophisticated (the PC had nothing better until the EGA cards came out). It was pure bit-mapped color graphics, 640x225 resolution. There was a major revision of the motherboard after about 2 years of production, the early models had a 5MHz 8088 and 3 banks of 64k each (192k total) memory, the later models COULD (but did not always) have an 8MHz 8088 and the memory banks could be 256MB chips per bank (768MB total) rather than 64k per bank. Models with the late motherboard (85-2806) could be upgraded to the faster CPU or larger memory if desired by changing some parts. The early motherboard (85-2653) could not be easily upgraded (plans for upgrading the early motherboard do exist, but it is a MASSIVE undertaking in terms of the number of changes, cuts and jumpers required. It takes a real masochist to undertake it). Barry Watzman [One of the architects of the Z-100 and the computer Product Line Director for both Heathkit and Zenith Data Systems from 1979-1983].