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Indiana University

ARCHIVED: What is Mach?

Based on BSD, Mach began as a Unix-like operating system developed by Carnegie Mellon University (CMU). Conceived in 1985 as a research initiative, work on Mach continued at CMU until 1994. A number of organizations and corporations have continued to develop Mach, and several major operating systems are currently based on the Mach microkernel, including:

  • Apple's Mac OS X, which is based on NeXT's OPENSTEP operating system

  • OSF/1, developed by the Open Group and incorporated into a number of Unix implementations, notably Tru64 UNIX. The Open Group calls its Mach descendant Mk.

  • Tenon Intersystems' MachTen, a Unix implementation that runs on top of Mac OS

  • The GNU Hurd, which is intended as a replacement for the Unix kernel; see GNU Hurd.

Mach's extremely portable microkernel handles low-level functions such as memory and thread management, multi-processor support, and interprocess communication and I/O. Higher-level functions, however, are left to OS-specific servers. The microkernel and servers perform the functions traditional kernels normally perform: catching and handling system calls. However, with Mach, calls are never allowed to access the hardware directly; that is reserved for the microkernel itself. While this arrangement can dramatically ease portability, it occasionally affects performance and breaks older software.

Though Mach is no longer an active project, Carnegie Mellon maintains a useful Mach project page with links to other resources.

For a forum of discussion about Mach, see the newsgroup comp.os.mach .