evaluation

Vagelis Hristidis (vagelis@cs.ucsd.edu)
Tue, 25 Apr 2000 02:17:08 -0700

On the Duality of Operating System Structures

This paper compares two main categories of Operating Systems. The first
category is the message based system , where we have a small, static number
of processes synchronized using messages, and the second is the procedure
oriented system, where we have a large ,dynamic number of small processes
synchronized with shared data.
The main conclusion of the paper is that the decision on which category to
choose is only based on the machine architecture and not on the
applications.
It is not obvious to me why a system with few processes should use messages
and one with many processes should use locks.
The paper describes nicely the duality between the two categories of
operating systems. It concludes by stating some differences in the machine
architecture. For example that a stack architecture would work better for
the procedure oriented model.

The Structuring of Systems using Upcalls

This paper discusses the idea of performing synchronous communication
between the processes that represent the layers of abstraction of a system.
Upcalls is a feature that permits the programmer to do either an
asynchronous signal or a procedure call for an upward call. The second half
of the paper talks about layers. It suggests organizing them as a collection
of subroutines which live in a number of tasks. The layer constructed this
way is called multi-task module. The main advantages of the synchronous
communication between layers are efficiency and simplicity. The main
disadvantage of the overall methodology is that an erroneous upper level may
leave a lower level in an inconsistent state.