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appb - The Mach System Appendix B In this appendix we...

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B Appendix The Mach System In this appendix we examine the Mach operating system. Mach is designed to incorporate the many recent innovations in operating-system research to produce a fully functional, technically advanced system. Unlike UNIX , which was developed without regard for multiprocessing, Mach incorporates multi- processing support throughout. Its multiprocessing support is also exceedingly flexible, accommodating shared-memory systems as well as systems with no memory shared between processors. Mach is designed to run on computer systems ranging from one processor to thousands of processors. In addition, Mach is easily ported to many varied computer architectures. A key goal of Mach is to be a distributed system capable of functioning on heterogeneous hardware. Although many experimental operating systems are being designed, built, and used, Mach satisfies the needs of the masses better than the others because it offers full compatibility with UNIX 4.3 BSD . As such, it provides a unique opportunity for us to compare two functionally similar, but internally dissimilar, operating systems. Mach and UNIX differ in their emphases, so our Mach discussion does not exactly parallel our UNIX discussion. In addition, we do not include a section on the user interface, because that component is similar to the user interface in 4.3 BSD . As you will see, Mach provides the ability to layer emulation of other operating systems as well; other operating systems can even run concurrently with Mach. B.1 History of the Mach System Mach traces its ancestry to the Accent operating system developed at Carnegie Mellon University ( CMU ). Although Accent pioneered a number of novel operating system concepts, its utility was limited by its inability to execute UNIX applications and its strong ties to a single hardware architecture, which made it difficult to port. Mach’s communication system and philosophy are derived from Accent, but many other significant portions of the system (for example, the virtual memory system and the management of tasks and threads) were developed from scratch. An important goal of the Mach effort was support for multiprocessors. 873
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874 Appendix B The Mach System Mach’s development followed an evolutionary path from BSD UNIX sys- tems. Mach code was initially developed inside the 4.2 BSD kernel, with BSD kernel components being replaced by Mach components as the Mach compo- nents were completed. The BSD components were updated to 4.3 BSD when that became available. By 1986, the virtual memory and communication subsystems were running on the DEC VAX computer family, including multiprocessor versions of the VAX . Versions for the IBM RT/PC and for Sun 3 workstations followed shortly; 1987 saw the completion of the Encore Multimax and Sequent Balance multiprocessor versions, including task and thread support, as well as the first official releases of the system, Release 0 and Release 1.
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