Originally released in 1983 by Science Management Corporation and later under Concept Omega Corporation, Thoroughbred/OS is a unique BASIC oriented multi-tasking multi-user operating system for the IBM XT and compatible systems.https://winworldpc.com/product/thoroughbred-os
It is designed to run on a dedicated system that powers a number of
serial terminals. It can power up to 16 terminals with the right
serial expansion cards. All of the applications are written in BASIC,
and the shell itself is an interactive basic interpreter.
Most computers these days are just an empty box without an operating system. But early microcomputers would often start up to BASIC in ROM, and by extending available command, BASIC would sometimes double as a command "shell". For example, loading Applesoft DOS on an Apple II would give you ROM BASIC but with access to disk commands. Thoroughbred/OS sort of mirrors that way of doing things.
Thoroughbred/OS seems to qualify as a full blown, although somewhat primitive, operating system.
It supports multi-tasking, multiple users, background processes, several high-end serial expansion devices, and supports a variety of terminal types.
All applications that run under this system must be written and stored in Thoroughbred's BASIC. While this means it does NOT support DOS programs, this ensures that all applications are well-behaved and capable of running in a multi-user environment.
It uses its own proprietary and unusual file system. It is neither DOS nor anything else.
The Thoroughbred/OS file system supports "directories". But they are not hierarchical and only up to 10 are "accessible" across all drives at any given time. Reconfiguring what directories are available is sort of like choosing drives to mount, and requires a reboot. You must manually specify how many maximum files each directory may hold. That is even weirder than CP/M's "user areas". It supports read and write file buffering.
This version supports the IBM AT and use of 360k, 720k, 1.2mb, and 1.44mb floppy disks. It also supports a tape backup device, and even contains a disk defragmentation tool.
I'm not sure if the underlying OS is directly or indirectly based on anything else. It looks very unique in all regards.
The installation requires a hard disk drive. It expects a standard IBM XT 10-megabyte hard drive, but can work with others. Thoroughbred/OS requires its own partition for its propriety file system. The setup is rather complicated, but this archive thankfully includes the manuals.
An annoyance is that Thoroughbred/OS is copy protected. It requires a serial dongle called the "Thoroughbred Passport". Without this dongle you are only allowed to start the OS seven times before it refuses. And you will need several reboots just for installation. Of course, with an emulator you can just revert the image.
Interestingly it seems that Thoroughbred/OS was supported for quite some time, well in to the era where most other non-DOS compatible IBM PC OSes had died off.
A separate product, "Thoroughbred BASIC" was available for DOS, Unix, and VMS. Although I am not sure, it seems unlikely the DOS product offered any multi-tasking capabilities.
So, in conclusion, this is a very unique little operating system for 8088/8086 based PCs.