The Multics virtual memory: concepts and design

The Multics virtual memory: concepts and design, A. Bensoussan, C. T. Clingen and R. C. Daley, Communications of the ACM, Vol. 15, NO. 5, May 1972, pp. 308 – 318.

As we might know, the use of on-line operating systems has been growing as well as the need to share information among system users. However, they share by the use of segmentation. This motivated the authors, such that, in order to take advantage of the direct addressability of large amounts of information which made possible by large virtual memories, the authors are motivated to develop a Multics (Multiplexed Information and Computing Service) to provide a generalized basis for the direct accessing and sharing of online information. There are two goals; the first goal is it must be possible for all on-line information stored in the system to be addressed directly by a processor. Another goal is that it must be possible to control access.

Regarding to the authors contributions, the authors have introduced an idealized memory by using the segmentation and paging features of the 645 assisted by the software features. Also, to take some advantages of existing mechanism , the Multics processes and the Multics supervisor were introduced The symbolic addressing conventions technique also provide an ease of use for users, such that a user can reference a segment’s pathname and supplying the rest of the pathname according to system conventions. Moreover, by making a segment known to a process and improve the segment fault handler have given the Multics a lot of performance.

The paper’s single most noticeable deficiency is that there are too many assumptions, so it makes the readers pretty confused of how to use the features of the Multics. The conclusion of the paper should summarize what the authors have contributed and how to improve it in the future work, instead of showing of user and supervisor view points. It would be good if the authors emphasize of how the selection algorithm work. For the question according to the paper, I would like to know how much it improves from the old fashion of the concept.
Lastly, I would rate the significance of the paper 3(modest) due to the fact that this paper is published 30 more years ago. It lacks of experimental and compare/contrast with the use of segmentation.

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