The Multics Virtual Memory: Concepts and Design As experience with use of on-line operating systems has grown, the need to share information among system users has become increasingly apparent. Many contemporary systems permit some degree of sharing. Usually, sharing is accomplished by allowing several users to share data via input and output of information stored in files kept in secondary storage. Through the use of segmentation, however, Multics provides direct hardware addressing by user and system programs of all information, independent of its physical storage location. Information is stored in segments each of which is potentially sharable and carries its own independent attributes of size and access privilege. Here, the design and implementation considerations of segmentation and sharing in Multics are first discussed under the assumption that all information resides in large, segmented main memory. Since the size of main memory on contemporary systems is rather limited, it is then shown how the Multics software achieves the effect of a large segmented main memory through the use of the Honeywell 645 segmentation and paging hardware. CACM May, 1972 Bensoussan, A. Clingen, C. T. Daley, R. C. operating system, Multics, virtual memory, segmentation, information sharing, paging, memory management, memory hierarchy 4.30 4.31 4.32 CA720502 JB January 31, 1978 11:24 AM 1753 4 2358 1754 4 2358 1892 4 2358 1901 4 2358 2085 4 2358 2095 4 2358 2218 4 2358 2277 4 2358 2317 4 2358 2319 4 2358 2329 4 2358 2358 4 2358 2358 4 2358 2358 4 2358 2358 4 2358 2377 4 2358 2373 4 2358 2372 4 2358 2380 4 2358 2434 4 2358 2499 4 2358 2501 4 2358 2582 4 2358 488 4 2358 2625 4 2358 2626 4 2358 2669 4 2358 2828 4 2358 2840 4 2358 2863 4 2358 2881 4 2358 2928 4 2358 2996 4 2358 3006 4 2358 3067 4 2358 274 5 2358 1746 5 2358 1751 5 2358 1753 5 2358 2358 5 2358 2358 5 2358 2358 5 2358 2377 5 2358 2625 5 2358 2626 5 2358 2669 5 2358 1471 6 2358 1471 6 2358 1746 6 2358 1746 6 2358 1749 6 2358 1751 6 2358 1753 6 2358 1901 6 2358 2017 6 2358 2358 6 2358 2358 6 2358 2358 6 2358 2358 6 2358 2377 6 2358 2438 6 2358 2625 6 2358 2629 6 2358