Network Operating Systems
What is An Operating System?
All computers need an operating system. An operating system is a set of programs which together control the computer. The jobs of an O.S. include:
1. Providing an interface which lets the user
control the file system
2. Provides services to programs, giving them access to
Well known PC operating systems include
Multi-tasking Operating Systems
A multi-tasking O.S. can do many jobs at the same time. For example, under Windows NT, I can
all at the same time.
(In fact - it’s a trick. One CPU chip can only do one job at any time. A PC with just one CPU seems to multi-task because of time-slicing. This is just a fancy way of saying that the CPU works for a few milliseconds on job #1, then for a few milliseconds on job #2, then #3, then #4, then back to #1 again, and so on.)
Clients and Servers
The workstations of a network may be referred to as clients.
We are already familiar with the concept of a server.
The Jobs of a Network Operating System
A network operating system must do all of the jobs of an ordinary operating system, and it must also:
Server Software and Client Software
A network operating system is divided into two parts
1. The software on the server
2. The software on each of the clients
The Network Software On The Server
A server runs a network operating system and no other software.
A Novell server...
runs Novell Netware. It does not run DOS or Windows. It cannot be used for any other jobs except being a server.
An NT server...
runs Microsoft Windows NT Server. The Server could be used for running ordinary applications while acting as a server, but this is unlikely.
The Network Software On The Client
The DOS operating system does not have networking built in. To use a DOS / Windows 3.1 machine as a network client it is necessary to add extra software - software that is supplied by the network operating system vendor.
Modern Microsoft PC operating systems, such as Windows 95, already have connectivity to Microsoft Servers built right in. No extra software need be added to the client.
Client Software: The Redirector
To redirect, is to send someone in a different direction.
When I am working on my PC, I can load files from local drives, such as C:, or server drives, such as H:. The redirector is a piece of software that makes this possible.
The redirector intercepts any calls to remote resources, and passes those calls to the network.
Client Software: The Designator
Maybe you already know that drives F:, G:, H:, I:, etc. do not really exists. It is a trick.
The server might have just one hard drive. F:, G:, H:, I: etc. are just names for places on that
disk.
The designator is a small program loaded into each client that does this trick. For example, maybe every time I type G:, the designator replaces what I type with "Server:C:\progs".
The mappings of the designator are made by the Network Administrator when he creates the user account. They are loaded into the client PC when the user logs in.
Server Software
The network operating system on the server does many jobs. These include:
1. Manage the sharing of resources.
Many users can share resources on a network. They share the server’s hard drives and the data and programs on them. They share printers.
All of this is made possible by the server’s N.O.S.
2. Managing users.
The administrator can add new users and delete old users.
3. Controlling permissions - what the users are allowed to do.
I can see my directory, but I cannot see yours. I can read the files on drive G: but I cannot delete them. I can print to this printer, but not to the one in the LRC.
All of this is controlled by my permissions. When the administrator made my account he sets what I can see and what I cannot see, what I can do and what I cannot do. He uses the Network operating system to control this.
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