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~(@]m THIS DOCUfolENT CONTAINS INFORHATION PROPRIETARY
ADVA 1 TO THE NATIONAL CASH REGISTER Cor'lPANY AND CONTROL
DATA CORPORATION, ITS CONTENTS SHALL NOT BE
DIVULGED OUTSIDE OF EITHER CO~'PANY NOR REPRODUCED
WITHOUT EXPlICIT PERHISSION OF THE DIRECTOR AND
GENERAL HANAGER, NCRICDC ADVANCED SYSTEr"S LABORATORY.
DATE: November 20, 1974
TO: R~' E; Wagner LO(';ATION: - rbI\A~L.-
FROM: Ell C.. Crary .-JZ-.-C <:!....-- LOCATION: ESCASL EXT: 57
SUBJECT: OS STRUCTURE-----'
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Atter our discu~sions durin~ my last trip, I came away with the
impression that some confusion exists concerning Address Spaces
and their relationship to Processor States, Asynchronous Processing
and Serialization of Access. Perhaps theconfusiQn~s only mine,
but I would like to express my understanding of these concepts
if for no other reason than to demonstrate its inadequacy and
thus the need for further doc~mentation.
Processor State is used to protect the OS environment from cor-
ruption by errant code of a less trusted nature; in particular,
to protect the OS from its user. In this context, the OS environ-
ment is a collection of services upon which the user code may make
requests. The user requests are normally of an explicit nature,
but may be implicit as a result of some signal. A page fault is
the most obvious case of an implicit service request.
With the advent of mass storage and larger memories, t~e OS grew
to include functions that are not services to be performed for
the user code, but are jobs in their own right.' These System Jobs
include spooling and job scheduling. A distinction ~ust be made
between system jobs and services as;they are structured in a
different manner within the framework of the OS.
Address'Spaces are used to define jobs, or in some systems, job-
~teps. The address space is the basic unit of accountability and
the unit to which resources are assigned. With the inception of
multi-programming, the address space also became a mechanism for
relocation ..
The tonfusion on the user of addr~ss space arises because it does
not always have a complete definition or cause total relocation.
We are apt-to lose si9ht of the relationship of the QSservices
to the user code. But if address space is considered from the
services point of view instead of the users, then we see that the
u.er resides in the same address space ..
R. E. Wagner -2- November 20, 1974
The point I wish