Pavana Yalamanchili (pavanay@hotmail.com)
Wed, 24 May 2000 21:25:53 PDT

The MULTICS Virtual Memory: Concepts And Design

This paper basically talks about the design and implementation
considerations of segmentation and sharing in Multics and how the Multics
software achieves the effect of a large segmented main memory through the
use of the Honeywell 645 segmentation and paging hardware. Through the use
of segmentation, Multics provides direct hardware addressing by user and
system programs of all information, independent of its physical storage
location. It does so by mainly satisfying two design goals that first it
must be possible for all on-line information stored in the system to be
addressed directly by a processor and hence referenced directly by any
computation and secondly, it must be possible to control access, at each
reference, to all on-line information in the system. Information is stored
in segments each of which is potentially sharable and carries its own
independent attributes of size and access privilege. Finally the paper
summarizes the important points discussed in this paper by grouping them
into two groups: the point of view of the user of the virtual memory, and
the point of view of the supervisor itself.

Machine Independent Virtual memory Management For Paged Uniprocessor And
Multiprocessor Architectures

This paper describes the design and implementations of virtual memory
management within the CMU mach operating system and the experiences gained
by the Mach kernel group in porting that system to a variety of
architectures. This paper compares Mach to previous work and concludes that
Mach provides a relatively rich set of virtual memory management functions
compared to systems like 4.3bsd UNIX or V system. Most of the Mach features
were derived from earlier operating systems. Mach demonstrated that it was
possible to implement sophisticated virtual memory management making only
minimal assumptions about the underlying hardware support. It also showed
that separation of machine independent and dependent memory management code
need not result in increased runtime costs and can in fact improve overall
performance of UNIX style systems. Along with the improvement of
portability, it also made possible a relatively unbiased examination of the
pros and cons of various hardware memory management schemes , especially as
they apply to the support of microprocessors. The paper also mentions some
modifications to be done with regard to the machine dependent code in
support for a new architecture.
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