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<td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">6.1</b></font></td>
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<td bgcolor="#336666" width="100%"><b><font face="Arial" size="2" color="#FFFFFF">
<b>Workstations and Servers</b></font></b></td>
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<td bgcolor="#669999" height="25"><b>
<font face="Arial" size="2" color="#FFFFFF">6.1.4</font></b></td>
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<td bgcolor="#669999" height="25" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">Introduction to NOS</font></strong></td>
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<font size="2" face="Arial">A computer operating system (OS) is the
software foundation on which computer applications and services run on
a workstation. Similarly, a network operating system (NOS) enables
communication between multiple devices and the sharing of resources
across a network. A NOS operates on UNIX, Microsoft Windows NT, or
Windows 2000 network servers.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font><p>
<font face="Arial" size="2">Common functions of an OS on a workstation
include controlling the computer hardware, executing programs and
providing a user interface. The OS performs these functions for a
single user. Multiple users can share the machine but they cannot log
on at the same time. In contrast, a NOS distributes functions over a
number of networked computers. A NOS depends on the services of the
native OS in each individual computer. The NOS then adds functions
that allow access to shared resources by a number of users
concurrently. </font></p>
<p>
<font size="2" face="Arial">Workstations function as clients in a NOS
environment. When a workstation becomes a client in a NOS environment,
additional specialized software enables the local user to access
non-local or remote resources, as if these resources were a part of
the local system. The NOS enhances the reach of the client workstation
by making remote services available as extensions of the local
operating system. </font></p>
<p>
<font face="Arial" size="2">A system capable of operating as a NOS
server must be able to support multiple users concurrently. The
network administrator creates an account for each user, allowing the
user to logon and connect to the server system. The user account on
the server enables the server to authenticate that user and allocate
the resources that the user is allowed to access. Systems that provide
this capability are called multi-user systems.</font></p>
<p>
<font face="Arial" size="2">A NOS server is a multitasking system,
capable of executing multiple tasks or processes at the same time. The
NOS scheduling software allocates internal processor time, memory, and
other elements of the system to different tasks in a way that allows
them to share the system resources. Each user on the multi-user system
is supported by a separate task or process internally on the server.
These internal tasks are created dynamically as users connect to the
system and are deleted when users disconnect.</font></p>
<p>
<font face="Arial" size="2">The main features to consider when
selecting a NOS are performance, management and monitoring tools,
security, scalability, and robustness or fault tolerance. The
following section briefly defines each of these features.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"></font></p>
<p>
<font size="2" face="Arial"><b>Performance</b><br>
A NOS must perform well at reading and writing files across the
network between clients and servers. It must be able to maintain fast
performance under heavy loads, when many clients
are making requests. Consistent performance under heavy demand is an
important standard for a NOS.</font></p>
<p>
<font size="2" face="Arial"><b>Management and monitoring</b><br>
The management interface on the NOS server provides the tools for
server monitoring, client administration, file, print, and disk
storage management. The management interface provides tools for the
installation of new services and the configuration of those services.
Additionally, servers require regular monitoring and adjustment.</font></p>
<p>
<font size="2" face="Arial"><b>Security</b><br>
A NOS must protect the shared resources under its control. Security
includes authenticating user access to services to prevent
unauthorized access to the network resources. Security also performs
encryption to protect information as it travels between
clients and servers.</font></p>
<p>
<font size="2" face="Arial"><b>Scalability</b><br>
Scalability is the ability of a NOS to grow without degradation in
performance. The NOS must be capable of sustaining performance as new
users join the network and new servers are added to support them.</font></p>
<p>
<font size="2" face="Arial"><b>Robustness/fault tolerance</b><br>
A measure of robustness is the ability to deliver services
consistently under heavy load and to sustain its services if
components or processes fail. Using redundant disk devices and
balancing the workload across multiple servers can improve NOS
robustness.</font></p>
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