This article is from the MachTen & CodeBuilder FAQ, by Jaime Julca firstname.lastname@example.org with numerous contributions by others.
MachTen is a Berkeley UNIX operating system with a Carnegie-Mellon Mach
kernel. It runs as an application on the Macintosh Operating System (MacOS).
The MachTen UNIX kernel supports a standard UNIX applications environment
which in turn supports hundreds of standard UNIX applications. The UNIX
operating system runs in concert with the Macintosh operating system. When
MachTen is running, you still have access to the Macintosh Finder desktop
and Macintosh applications, such as a Macintosh spreadsheet or desk
Even though MachTen gives the appearance of being just another Macintosh
application, its operation is more like that of a co-resident operating
system. MachTen and MacOS share the processor -- when MachTen has control,
it pre-emptively multitasks the UNIX applications; when MacOS has control,
it runs the Mac applications using its cooperative sharing.
Since MachTen runs on top of MacOS, there is no need to partition the hard
drive or to install separate MachTen-specific device drivers. MachTen maps
the UNIX file system to the MacOS file system and uses the MacOS device
drivers. This means that there is a single, consistent file system and that
third party devices, such as network controller boards, automatically run
In addition, Power MachTen has its own native fast file system (implemented
within a single Macintosh file) that gives UNIX operations a significant
MachTen is a full-fledged operating system that, for portability reasons,
uses as much of the device driver software that's available in the
Macintosh. Where necessary, it will operate directly with the hardware.