OS-9

OS-9® is the name of a family of Unix-like operating systems developed by Microware Systems Corporation. The first version ("level one") was written in assembly language for the Motorola 6809 processor, and provides a single 64K address space in which all processes ran; a later 6809 version ("level two") takes advantage of memory mapping hardware.

Later, OS-9/6809 was converted to Motorola 68000 assembly language and extended, and a still further extended version was written mostly in C for portability. (The portable version was initially called OS-9000.) The later versions lack the memory mapping facilities of OS-9/6809 Level Two; to them, there is a single flat address space that all processes share, and memory mapping hardware, if present, is mostly used to ensure that processes access only that memory they have the right to access.

OS-9 has a similar notion of process and I/O path to Unix, but there are some significant differences:

The file system is not a single tree, but instead is a forest with each tree corresponding to a device.
OS-9 does not have a Unix-style fork()--instead it has a system call to create a process running a specified program.
OS-9 processes keep track of two "current directories" rather than just one; the "current execution directory" is where it will by default look to load programs to run.
OS-9 has had a modular design from the beginning, influenced by the notions of how the designers of the 6809 thought software would be sold in the future as described in a three-part series of articles in Jan-Mar 1979 Byte magazine. As a consequence of the design, programs to run under OS-9 use position-independent code.

(The module structure perhaps merits more explanation: OS-9 keeps a "module directory", a list in memory of modules that are in memory either by being loaded or by being found in ROM during an initial scan at boot time. When one types a command to the OS-9 shell, it will look first for a module by the specified name and run it if there is one or look on disk for an appropriately named file if not. In OS-9/6809 and OS-9/68000, the module directory is flat, but OS-9000 made the module directory tree-structured. The shell under OS-9000 looks for an MPATH environment variable analogous to PATH indicating a sequence of module directories in which to look for modules. Modules are not only used to hold programs, but can also be created on the fly to hold data, and are the way in which OS-9 supports shared memory.)

OS-9/6809 ran on Motorola EXORbus systems using the Motorola 6809, SS-50 and SS-50C bus systems from companies such as SWTPC, Gimix, and Smoke Signal Broadcasting, STD-bus 6809 systems, and personal computers such as the Fujitsu FM-7 and FM-77 and, probably best known, the various models of the Tandy Color Computer. (Actually, it still runs; the Tandy Color Computer still has users and an annual conference, the Nth Annual "Last" Chicago CoCoFest, where N == 11 in 2002. A group of Canadian programmers rewrote OS-9/6809 Level II for the CoCo 3 for efficiency and to take advantage of the native mode of the Hitachi 6309, and serious CoCo users typically have the 68B09E in the CoCo 3 replaced with a 6309E and are running the rewrite, called "NitrOS9.")

The various versions of OS-9/68000 run on a wide variety of 68000 family platforms, including the Sharp X68000 in Japan and some personal computers intended by their designers as upgrades from the Color Computer (e.g. the 68070 or 68340-based MM/1, and other computers from Frank Hogg Laboratories and Delmar Co.). OS-9000/80x86 can be run on Intel-based PCs. OS-9000 has also been ported to the PowerPC, MIPS, some versions of Advanced RISC Machines' ARM processor, and some of the Hitachi SH family of processors.

In 1999, nineteen years after the first release of OS-9, Apple Computer named a version of the operating system for the Macintosh "Mac OS 9". Microware sued Apple that year for trademark infringement, but a judge rejected this claim, dismissing the suit the following year. The judge said that there is little chance for confusion, but one still periodically finds postings to comp.os.os9 from Macintosh users who are at the very least confused about the purpose of the newsgroup.

the following text was moved from OS 9 and needs to be merged

OS-9 is a real-time, multi-tasking, multi-user operating system developed largely for the embeddable market by Microware for the Motorola 6809 microprocessor. 1

OS-9 was based loosely around the UNIX system, and had many of the same concepts.

As well as being designed for the embedded computer market, OS-9 was available for the Dragon 64 home computer in the 1980s. Applications such as a WYSIWYG word processor, and a spreadsheet (based on VisiCalc) etc were available for OS 9. It wasn't unknown to have several instances of a word processor and spreadsheet running at the same time, with two people using it on a 64kB Dragon 64 running a 0.9MHz 6809 processor. (The first user would use the normal Dragon 64 keyboard/monitor, the second user would use a VT52 terminal connected to the RS-232 serial port.

OS-9 had many innovative features because of its ability to run on a very low (by 2002 standards) specification computer. For instance, it supported dynamically loadable and unloadable device drivers so they only used memory when they were actually in use, and it handled code and data memory separately, so if you ran 5 copies of the word processor, only one copy of the program would be in memory with 5 different memory blocks for the data for the different copies.

OS-9 Level II also had a memory block switching architecture where a larger memory space could be switched in and out of the CPU 64k memory space as required (in 4kB block sizes), thus allowing even more applications to be run if the appropriate hardware was available.

The name "Mac OS 9" is also used for a version of Mac OS, although this usage post-dates by many years Microware's.