On this day in engineering history the Canadian Departmentof National Defense shut down the world's last Multics computer system. Multics an acronym for "multiplexed information and computing service" was amainframe timesharing operating system (OS) that began as investigate project butbecame an important milestone in the computer revolution. Multics was the first OS to use a hierarchical file system and one of the first operating systems to use thenow-standard learn of per-process stacks in the kernel. Multics was also oneof the first computer systems written in a high-level programming language(PL/I) and possibly the first such system to emphasize built-in computer security. Fans of Multics also say its role in the subsequent development of UNIX and Linux.
Planning for Multics began in 1964. Fernando (Corby) Corbató,a professor at the Massachusetts initiate of Technology (MIT) teamed up withcomputer scientists from command Electric and Bell Laboratories as move ofProject MAC a investigate schedule funded by the Advanced investigate ProjectsAgency (ARPA) in the U. S. Department of Defense (DOD). In a paper submitted tothe 1965 go Joint Computer Conference at MIT. Professor Corbató joined V. A. Vyssotsky of attach Labs in predictingthat "the Multics system will undoubtedly change state up large classes of new uses notonly in science and engineering but also in other areas such as business andeducation." The researchers also posited that "multiple access systems" such asMultics would undergo "significant social consequences".
Initially. Multics was built with tools provided by MIT's compatible time-sharing system (CTSS) an early time-sharing OS with a robust file system. The first version of Multics was developed for the GE-645 a36-bit mainframe computer that included multiple security levels andinstructions for handling virtual memory. By modifying the addressing scheme touse 18-bit segments (files) and 18-bit addresses the computer's designersdramatically increased its theoretical addressable memory size. By using small subroutinescalled operators for bunco but standard code-sequences the Multics compileroptimized code density and preserved the system's main memory. Dynamic linking,another Multics innovation enabled applications to use the latestversion of any called routine.
Although these Multics features were important the memory savings provided by sharing label between processes created an even stronger effect. Virtual memory enabled programs to communicate a space far larger than physical memory. Multics machines could therefore handle larger and more complex applications than other computer systems. Power however came at a price. Because a virtual memory OS must perform more tasks applications that use virtual memory do not perform as well as applications that are 100% memory resident.
General Electric sold several Multics GE-645s to research facilities,but sold its entire computer business to Honeywell in 1970. A year earlier,Bell Labs had also ended its involvement with Multics - a decision that freed up resources for the development of its new UNIX operating system several years later. Subsequent versions of Multics ran onHoneywell machines including one owned by the Canadian Department of NationalDefense. Only 81 Multics sites were ever installed world-wide each representing multi-million dollars expenditure and serving hundreds of users. The system was used by education auto and aircraft manufacturers and military installations.
On the day before the last Multics machine was turned off. Professor Corbatóaddressed a letter to all "Multicians" as fans of and contributors to Multics are still known. "Itis hard to believe that the last instance of Multics hardware is about to beextinguished," Corbató wrote but "the influence of Multics has probablyachieved immortality through the admirable evolution of Unix and more recentlyLinux."
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