Last update Feb 24 2019. Contents copyright Herb Johnson 2019, except quoted materials copyright by the authors or producers. Corrections are appreciated. Further dicussion of 21st century interest in Intel's ISIS-II is on this linked Web page. - Herb
The development of MS-DOS software for the IBM-PC of 1983, was apparently done on Intel Multibus based computers, running their ISIS-II operating system and various 8086 assemblers and PL/M compiler. An article about this was produced and posted on the "os2museum.com" Web site. Exerpts relevant to Intel and ISIS-II are copied here. Links in the document were updated in 2018. Refer to the original article for more details. - Herb Johnson
ISIS-II
ISIS-II ran on top of 8080, Intel’s famous 8-bit CPU. It was an operating system somewhat similar to CP/M in structure, but by no means compatible. It was, perhaps surprisingly, written not in 8080 assembly but in PL/M, a high-level programming language developed for Intel by Gary Kildall in 1972. ISIS itself was first written around 1976 and upgraded to ISIS-II for floppy-based systems; it appears that ISIS was developed at Intel after Gary Kildall left to start Digital Research and commercialize CP/M (something Intel was not interested in).
Amazingly enough, there’s an ISIS-II simulator which can be used to run 8-bit software designed for the 8080 on modern x86 systems. As it turns out, the ISIS-II was quite reasonably designed and the software running on it cleanly written. All I/O was file-based (using FCBs, not file handles!) and console access was TTY-like, which means the tools can be transplanted onto the command shell of a modern OS.
"[the simulator] currently builds and runs on 32-bit Linux [and now 64-bit as of 2019 - Herb]. It was originally written back in the 80s for DOS, but I haven’t done the necessary work to update it to work on Win32." - Mark Alexander, 2018 [See recent notes on my ISIS Web page. - Herb]
One curiosity of ISIS-II is that it used OMF (Object Module Format popularized by Microsoft’s DOS development tools) not only for object files but also for the executables loaded by ISIS-II into memory. It helps that at least some tools (e.g. the dmpobj utility shipped with the Open Watcom compilers understand the overall file structure even without knowledge of the meaning of 8080-specific records. With such tools it’s easy to verify the integrity of the files.
Extracting the Files
Okay, so there’s a working simulator, but what about the ASM86 files? The simulator works with host OS files, not with ISIS-II disk images. So the ASM86 executables somehow need to be extracted before they can be used.
As luck would have it, the ISIS-II disk format is quite well documented for such an antique and relatively obscure system. The OS/2 Museum developed a simple utility to take a raw image of an ISIS-II disk and break it down into individual files. Here's a local copy of that small program.
It’s worth mentioning that the ISIS-II had no concept of time and the files on ISIS-II disks therefore have no timestamps (clearly Intel was not yet ready for the wonders of ‘make’!). That makes it a bit difficult to determine the age of the files. The copyright messages embedded in the files hint that the newer ASM86 V2.1 was released in 1980 and V2.0 in 1979.
Running 1979 Tools 35 Years Later
With the ISIS-II simulator, it is very easy to run ASM86 V2.0, more or less exactly 35 years after it had been released. Well, that’s after fixing the simulator to load ASM86 properly—one of the overlays includes an object record loading data at a low address, which the simulator rejected, loaded the module only halfway, and soon thereafter crashed.
- Michal Necasek, exerpts from article
Copyright © 2019 Herb Johnson