Multi-Environment Real-Time

Multi-Environment Real-Time

Company / developer	Bell Labs[1]
OS family	Real-time operating systems
Marketing target	Real-time computing applications
Supported platforms	PDP-11[1]
Kernel type	Microkernel[1]

The Multi-Environment Real-Time (MERT) operating system was one of the earliest to be constructed using an organizational concept that later became known as a "micro-kernel".

Multi-Environment Real-Time was created in the 1970s at Bell Labs, and was a spinoff of Unix. It ran on Digital Equipment Corporation PDP-11 computers (models 11/45 and 11/70). A version called Duplex Multi Environment Real Time (DMERT) was the operating system for the AT&T 3B20D telephone switching minicomputer; DMERT was renamed UNIX-RTR (Real-Time Reliable) in 1982.^[2]

Although it was not exactly a micro-kernel as they are today, it was a definitely not a "monolithic kernel"; it was a major step down the road to micro-kernels (Altinsel). MERT was an operating system which was divided up into several semi-independent components, all of which ran on a lower-level "kernel" (as they described it).

The kernel provided only the lowest-level basic mechanisms (memory management, process scheduling, etc.); the other components needed for an operating system (e.g. a file system) were constructed as processes which ran on top of the kernel. Inter-process communication (IPC) was done with messages, event flags, shared memory and shared files.^[1]

MERT was also intended to be used in real-time applications, and had a number of features to meet this goal. Process scheduling had real-time mechanisms, as did the file system.

References

1. ^ ^{a b c d} "MERT - a multi-environment real-time operating system". Proceedings of the fifth ACM symposium on Operating systems principles. http://doi.acm.org/10.1145/800213.806519. http://portal.acm.org/citation.cfm?id=806519. Retrieved 2008-08-18. 
2. ^ D. E. Bodenstab, T. F. Houghton, K. A. Kelleman, G. Ronkin, and E. P. Schan (October 1984). "UNIX Operating System Porting Experiences" (PDF). AT&T Bell Laboratories Technical Journal, Vol. 63, No. 8 Part 2. pp. 9. http://www.cs.bell-labs.com/who/dmr/otherports/newp.pdf. Retrieved 2008-08-18. 

• D. L. Bayer, H. Lycklama, MERT - a multi-environment real-time operating system, (Fifth ACM Symposium on Operating Systems Principles, Austin, Texas, 1975)
• H. Lycklama, D. L. Bayer, The MERT Operating System (The Bell System Technical Journal, July–August 1978, Vol. 57, No. 6, Part 2)
• J. O. Becker, The 3B20D PROCESSOR and DMERT Operating System (The Bell System Technical Journal, January 1983, Vol. 62, No. 1, Part 1)
• Altinsel, M. 1983. "Resourceful Uses of M.E.R.T". Scientific Philosophy, October 6, 1983

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