The GE 645 mainframe computer was a development of the

GE 635 The GE-600 series was a family of 36-bit mainframe computers originating in the 1960s, built by General Electric (GE). When GE left the mainframe business the line was sold to Honeywell, which built similar systems into the 1990s as the division ...

for use in the

Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of ...

project. This was the first computer that implemented a configurable hardware protected memory system. The original CTSS was implemented on a modified IBM 7094 with two banks of memory and bank-switching between user and supervisor mode, i.e. programs running in the A-core memory bank had access to instructions that programs running in the B-core bank did not. The Multics operating system implemented

multilevel security Multilevel security or multiple levels of security (MLS) is the application of a computer system to process information with incompatible classifications (i.e., at different security levels), permit access by users with different security clearan ...

(MLS) on a GE 635 by running a simulator of the 645 starting on October 18, 1965, in the MIT Tech Center. This simulated environment was replaced by the first 645 hardware in 1967. The

GECOS General Comprehensive Operating System (GCOS, ; originally GECOS, General Electric Comprehensive Operating Supervisor) is a family of operating systems oriented toward the 36-bit GE/Honeywell mainframe computers. The original version of GCOS wa ...

operating system was fully replaced by Multics in 1969 with the Multics supervisor (master mode now known as

kernel mode In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security). Compute ...

) separated by

protection ring In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security). Computer ...

s with "gates" allowing access from user mode. A later generation in the form of the 645F (F for follow-on) wasn't completed by the time the division was sold to

Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...

, and became known as the

Honeywell 6180 The Honeywell 6000 series computers were rebadged versions of General Electric's 600-series mainframes manufactured by Honeywell International, Inc. from 1970 to 1989. Honeywell acquired the line when it purchased GE's computer division in 197 ...

. The original access control mechanism of the GE/Honeywell 645 were found inadequate for high speed trapping of access instructions and the re-implementation in the 6180 solved those problems. The bulk of these computers running

time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence ...

on Multics were installed at the NSA and similar governmental sites. Their usage was limited by the extreme security measures and had limited impact on subsequent systems, other than the protection ring. The hardware protection introduced on this computer and modified on the 6180 was later implemented in the Intel 286 computer processor as a four-layer protection ring, but four rings was found to be too cumbersome to program and too slow to operate. Protection ring architecture is now used only to protect kernel mode from user mode code just as it was in the original use of the 645.

References

{{reflist

External links

GE-645 Circuit Board

600 __NOTOC__ 600 ( DC) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar. The denomination 600 for this year has been used since the early medieval period, when the Anno Domini calendar era became the ...

Transistorized computers 36-bit computers Computer-related introductions in 1967 Time-sharing