Software spotlight: Zenith MS-DOS 2 Programmers Utility Pack

edited April 2016 in Software Spotlights
The Zenith MS-DOS Programmer's Utility Pack V 2 contains Zenith source code and compiler utilities needed for building an MS-DOS 2 BIOS (IO.SYS file) for use with the Zenith Z-100 (not IBM hardware compatible), the Zenith Z-100 PC (IBM hardware compatible), and the Zenith Z-100 PC running in Z-100 compatibility mode.

To assist you in actually doing anything with this code, the 800+ page honking thick manual documents MS-DOS structures, the interfaces for the applicable hardware platforms, and the compiler utilities. ... ility-pack


The Zenith Z-100 systems came from an environment where extensive hardware modification and customization was quite common. The original Zenith Z-100 Series (Z-110/Z-120) used an S-100 expansion bus, which enabled it to make use of many existing S-100 expansion cards. These systems were also sold under the Heath brand name as unassembled kits.

From what I can tell, these Zenith Programmers Utility Packs were relatively common. They may have been bundled with systems or other software. But off hand, I'm not aware of any other OEM that made such sources commonly available to the end users.

The DOS "BIOS", more commonly referred to as the "IO.SYS" file, is sort of like a pack of device drivers for things like low-level disk I/O and console I/O. Because it exists as a seperate file, this enables the MS-DOS kernel file ("MSDOS.SYS") to remain mostly unchanged.

This architecture was adopted from Digital Research's CP/M, where they also used a CP/M "BIOS" and a seperate CP/M kernel (or "nucleus" as Digital Research called it).

In earlier systems the BIOS was entirely contained within a software file. Any ROM was often only used for bootstrapping and then jettisoned. When IBM designed the IBM PC, they instead put part of this BIOS in ROM, partly to support ROM BASIC, and perhaps to save RAM. As a result, we often refer to a PC's firmware ROM as "BIOS".

The Zenith Z-110 and Z-120 contain most of their BIOS in the IO.SYS file. In versions for these systems, this code talks directly to the disk controller chips.

The later IBM PC compatible Z-150, Z-160, etc machines provide a mostly IBM PC compatible ROM BIOS. Therefore the Z-100 PC DOS BIOS uses that instead.

As I vaguely recall, supposedly the MS-DOS 1.25/2.00 source code that was published a while back was missing BIOS code. No idea if this could help or not.

Wanted: Reportedly, there is also a Zenith MS-DOS 3 Programmers Utility Pack. I'd also expect there was probably a MS-DOS 1.25/Z-DOS Programmers Utility Pack.

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