is not easy to shake off the image of "feudal user" that guy that shows credentials the doors of the wall, and once in their domains, have them as master. However ... conceive it otherwise.
USER SESSION does not directly involve
For a system which is accessible to several people at once arises the need for the concept of "session."
A SESSION represents a "working day" from the perspective of who is using the system via Terminal. At one point, N people will be connected to terminal N and therefore N must be separate sessions, one for each. If, in particular, all are using the same program, then there will be N instances of the same program which implies N separate data areas: one for each instance, ie, one for each session, or what is equal, one for each visitor.
Note that I said "visitors", not "user", this is because users need to define the concept derives directly SESSION but the concept of "private property" (to those users of the system on certain media, for example files). From the perspective of the OS, users are entities registered in advance in data structures designed for that purpose. In the presence of "private property", each session will belong to a user (previously registered) which will be identified (say who) before they can gain access to their own resources.
Another possibility is to give up the "private property." In such cases, all system resources are the heritage of all who visit and then the concept of user automatically loses its meaning.
SESSION concept, however, prevalce, it is still necessary that several people work with the system at the same time without interfering with each other actions.
Imagine all the people sharing all the World
The experience of a shared system without privileges to all visitors with us today on the Internet (Wikipedia is a good example), but try to imagine a system like Heritage / 1 in 1972.
Say a minicomputer Heritage / 1 is installed in a software production company. There are eight programs each with its corresponding terminal. All resources of the machine (especially the peripheral tapes, impersoras etc) are shared so that arbitrage should exercise any OS to prevent, for example, a print out with two servings intertwined different programmers.
The arbitration, however, does not imply property relations on resources but only a mechanism to bring order into licentiousness. For example, if two processes have requested the use of the printer, then one will have to wait until the other end.
Short of Anarchy
coloquemas Now a Heritage / 1 in a public library. The Library Catalog recycle in a database accessible to visitors through four terminals installed in the lounge. The visitor does not have to be identified, simply consult the catalog directly from either terminal, and not only performs read operations but also leave comments, suggest books not in the catalog, etc., provided on an "anonymous" (from system perspective) which does not prevent someone leave your name and phone number voluntarily.
Updating the Catalog, however, can not left to the visitors as this is a professional task, so that the system offers some programs for visitors and others to librarians.
This can be solved based on the terminal (port), ie without need for early adopters. The OS can create a table of available software for each of which specifies the terminals (ports) licensed to serve as an interface. In this way, visitors will never gain access to the catalog maintenance program.
How is this related to SESSION?
When the visitor enters the system through a terminal, you create a session tied to that terminal, the shell presents a list programs available to "him" (actually, for that port.) Apart from the catalog may have other utility programs such as math, the user could run these programs, get results, send to the printer (shared with others, you may have to queue) and then close the session or not.
terminals used by librarians operate similarly, except that they will have access to both the catalog and to the maintenance of the programs.
And what is the advantage of all this?
The advantage is not having to manage users within the OS, which represents a tremendous savings in terms of development effort and maintenance system.
We have seen that a system can be accommodated in a cooperative work such as software development and a public service with a library. In general you will find a place in a facility where the computer provides specific services to a specific audience, as was common until the early 80s.
Today, this type of service (purpose, visitors are not privileged) is still common, especially on the Web. Only that level of implementation itself uses the concept of a user for security reasons and, above all, because operating systems are used as implicit.
CONCLUSIONS
In a time-sharing system SESSION need the concept of building a "framework" for each terminal separately. The concept of users, however, is optional.
If not required "private property" (resource users), the concept of user is more. Implement only consiguiría imnecesariamente overload the system complexity.
If privacy is required the Administrator for certain system resources (eg, maintenance programs and configuration files), it is necessary to see the manager as a "user": just Restrict these resources to those terminals intended for administrators.
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