Last Updated on: 8th November 2023, 05:10 pm

Web site: (not active)
Origin: USA
Category: Workstation
Desktop environment: CLI
Architecture/Platform: Zliog Z80
Based on: Independent
Wikipedia: HDOS
Media: Live
The last version | Released: 3.02 | 1986

HDOS (Heath Disk Operating System; also: HeathDOS) – an open-source microcomputer operating system released in 1978, originally written for the Heathkit H8 computer system and later also available for the Heathkit H89 and Zenith Z-89 computers.

HDOS was originally written for Heath Company’s H-8 computer system when a 5-1/4 inch floppy disk subsystem was added as a peripheral to the model. HDOS was written in 1978 by J. Gordon Letwin.

Like many microcomputer systems of that period, the H-8 has read-only memory (ROM) at the bottom of addressable memory. However, instead of an interpreter for the BASIC language as was common on other systems such as Apple II and Radio Shack TRS-80, the H-8 locates input/output (I/O) ports and routines, some hard-coded utility routines, common functions, and scratch RAM in this area.

This ROM occupies 8K, hence HDOS can handle up to 56K of free RAM. It also runs without changes on Heath/Zenith’s popular Z-89 and Z-90 microcomputers.

In April 1988, at the request of Kirk L. Thompson, publisher of THE STAUNCH 8/89’er, a newsletter for the H-8 and Z-89/90, Heath released HDOS 2.0 into the public domain. This release included assembler source code, executable programs, and documentation. HDOS 3.0 was also enhanced further by Richard Musgrave as version 3.02. Thompson coordinated the melding of this upgrade with some 1,000 pages of documentation written by Daniel N. Jerome in 1990. The new manual was based on the old now-public-domain manual for HDOS 2.0, the minimum documentation that accompanied HDOS 3.0, and additional material provided by Musgrave.

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