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Revision Date Username Comment
929 Dec 2015 - 17:55ThomasMisa 
829 Dec 2015 - 17:46ThomasMisa 
729 Dec 2015 - 17:11ThomasMisa 
603 Oct 2013 - 15:41norqu036? 
519 Apr 2013 - 11:25NicLewis 
412 Mar 2013 - 10:44NicLewis 
305 Mar 2013 - 10:07NicLewis 
225 Feb 2013 - 10:41NicLewis 
121 Feb 2013 - 09:24NicLewis 

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You are here: UMWiki>CBI_ComputerSecurity Web>Systems>SystemsCmmpHydra (29 Dec 2015, ThomasMisa)

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C.mmp was a Carnegie Mellon University multiprocessor computer system meant to demonstrate the cost/performance advantages of multiprocessor-based computers derived from the relatively inexpensive minicomputers that were then becoming available. Although Wikipedia's article states that the "C" in the system name stood for CPU, this assertion is not supported by documents from the project team. A 1973 paper by project leader Bill Wulf and colleagues suggests that "C" stood instead for Carnegie Mellon ("This paper describes the design philosophy of HYDRA -- the kernel of an operating system for C.mmp, the Carnegie-Mellon Multi-Mini-Processor . . .")(1) while a semi-official book publication alternatively suggests that "C" stood for computer ("Hydra runs on C.mmp (Computer.multi-mini-processor) . . .").(2) It is generally accepted that "mmp" stood for "Multi-Mini-Processor."

The C.mmp employed up to sixteen DEC PDP-11 minicomputers which were interconnected through a crossbar switch. This allowed each of the sixteen modules to share resources, including memory and peripherals. Carnegie Mellon modified the PDP-11 hardware to meet the needs of the project, attempting to overcome limitations of hardware that was not intended for multiprocessor compatibility.

Hydra was the C.mmp's object-oriented multi-user operating system, with system resources represented as objects. Hydra was an early fault-tolerant system, as it would remove a memory block from system use upon the detection of a fault. Likewise, the hardware attempted to increase system reliability through monitoring of each processing element. Upon detection of abnormal behavior, a processor would be removed from system use, and would conduct diagnostics until its performance proved satisfactory. However, reliability remained an issue with C.mmp, mostly due to the number of linked computers increasing the likelihood of failure, and timing errors in the modified hardware causing system errors.(3)(4)

Additional Resources:

  • lock William A. Wulf and C. G. Bell, "C.mmp--A multi-mini-processor," Fall Joint Computer Conference 1972 (AFIPS Conference Proceedings, December 5-7, 1972).


1 : Wulf et al. "HYDRA -- the kernel of a multiprocessor operating system" (1973), quote in abstract, at external CMU repository

2 : lock Henry M. Levy, The Hydra System (Digital Press, 1984), quote p. 103. (Login required)

3 : lock Henry M. Levy, The Hydra System (Digital Press, 1984), 103-105, 109. (Login required)

4 : lock Daniel P. Siewiorek, et al., "A Case Study of C.mmp, Cm*, and C.vmp: Part I--Experiences with Fault Tolerance in Multiprocessor Systems," Proceedings of the IEEE 66, no. 10 (October, 1978), 1178, 1180-1183. (Login required)

Topic revision: r9 - 29 Dec 2015 - 17:55:38 - ThomasMisa
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