Today, OS-9 is a product name used by both a Motorola 68000-series machine language OS and a portable (PowerPC, x86, ARM, MIPS, SH4, etc.)
In 1983, OS-9/6809 was ported to Motorola 68000 assembly language and extended (called OS-9/68K); and a still later (1989) version was rewritten mostly in C for further portability.
The OS-9 kernel loads programs (including shared code), and allocates data, wherever sufficient free space is available in the memory map.
Programs, device drivers, and I/O managers under OS-9 are all 'modules' and can be dynamically loaded and unloaded (subject to link counts) as needed.
System Industries, a third-party provider of DEC compatible equipment, used a 68B09E processor running OS9 in its QIC (quarter-inch cartridge) tape backup controllers in VAX installations.
The best known hardware (due to its low price and broad distribution) was the TRS-80 Color Computer (CoCo) and the similar Dragon series.
The Toronto PET Users Group sponsored a HW/SW project which included a daughter board with an MMU as well as the OS-9 distribution disks.
Many third-party interactive applications have been written for it, such as the Dynacalc spreadsheet, the VED text formatter, and the Stylograph and Screditor-3 WYSIWYG word processors.
Around the same time, Microsoft approached Microware for acquisition of the company primarily because it was attracted by CD-RTOS, the CD-i operating system.
The vast majority of the operating system kernel was rewritten in C leaving a handful of hardware-dependent parts in assembly language.
The OS-9000/680x0 was a marketing failure and withdrawn very quickly, probably because few customers wanted to try the fatter and slower operating system over the existing OS-9/680x0 proven record of stability.
Microware sued Apple that year for trademark infringement,[4] although a judge ruled that there would be little chance for confusion between the two.
On February 21, 2013, Microware LP (a partnership formed by Freestation of Japan, Microsys Electronics of Germany and RTSI LLC of the USA) announced that they signed an Asset Purchase Agreement to buy the rights to the names Microware, OS-9 and all assets from RadiSys.
When compared with more modern operating systems: OS-9's real-time kernel allows multiple independent applications to execute simultaneously through task switching and inter-process communication facilities.
Aging artificially increases the effective priority of threads in the active queue as time passes.
Another difference is that in OS-9, grandparent directories can be indicated by repeating periods three or more times, without any intervening slashes (a feature also found in 4DOS/4OS2/4NT/TC).