the native OS in each individual computer. The NOS
then adds functions that allow access to shared resources by a
number of users concurrently. 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. 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. 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. 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.
Performance
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.
Management and monitoring
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. Security
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.
Scalability
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. Robustness/fault
tolerance
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.
Content 6.1
Workstations and Servers 6.1.5 Microsoft NT,
2000, and .NET Since the release of Windows 1.0 in November
1985, Microsoft has produced many versions of Windows operating
systems with improvements and changes to support a variety of
users and purposes. Figure summarizes the current Windows OS.
NT 4 was designed to provide an environment for mission
critical business that would be more stable than the Microsoft
consumer operating systems. It is available for both desktop
(NT 4.0 Workstation) and server (NT 4.0 Server). An advantage
of NT over previous Microsoft OSs is that DOS and older Windows
programs can be executed in virtual machines (VMs). Program
failures are isolated and do not require a system restart.
Windows NT provides a domain structure to control user and
client access to server resources. It is administered through
the User Manager for Domains application on the domain
controller. Each NT domain requires a single primary domain
controller which holds the Security Accounts Management
Database (SAM) and may have one or more backup domain
controllers, each of which contains a read-only copy of the
SAM. When a user attempts to logon, the account information is
sent to the SAM database. If the information for that account
is stored in the database, the user will be authenticated to
the domain and have access to the workstation and network
resources. Based on the NT kernel, the more recent Windows 2000
has both desktop and server versions. Windows 2000 supports
“plug-and-play” technology, permitting installation of new
devices without the need to restart the system. Windows 2000
also includes a file encryption system for securing data on the
hard disk. Windows 2000 enables objects, such as users and
resources, to be placed into container objects called
organizational units (OUs). Administrative authority over each
OU can be delegated to a user or group. This feature allows
more specific control than is possible with Windows NT 4.0.
Windows 2000 Professional is not designed to be a full NOS. It
does not provide a domain controller, DNS server, DHCP server,
or render any of the services that can be deployed with Windows
2000 Server. The primary purpose of Windows 2000 Professional
is to be part of a domain as a client-side operating system.
The type of hardware that can be installed on the system is
limited. Windows 2000 Professional can provide limited server
capabilities for small networks and peer-to-peer networks. It
can be a file server, a print server, an FTP server, and a web
server, but will only support up to ten simultaneous
connections. Windows 2000 Server adds to the features of
Windows 2000 Professional many new server-specific functions.
It can also operate as a file, print, web and application
server. The Active Directory Services feature of Windows 2000
Server serves as the centralized point of management of users,
groups, security services, and network resources. It includes
the multipurpose capabilities required for workgroups and
branch offices as well as for departmental deployments of file
and print servers, application servers, web servers, and
communication servers. Windows 2000 Server is intended for use
in small-to-medium sized enterprise environments. It provides
integrated connectivity with Novell NetWare, UNIX, and
AppleTalk systems. It can also be configured as a
communications server to provide dialup networking services for
mobile users. Windows 2000 Advanced Server provides the
additional hardware and software support needed for enterprise
and extremely large networks. Windows .NET Server is built on
the Windows 2000 Server kernel, but tailored to provide a
secure and reliable system to run enterprise-level web and FTP
sites in order to compete with the Linux and UNIX server
operating systems. The Windows .NET Server provides XML Web
Services to companies which run medium to high volume web
traffic.
Content 6.1 Workstations and
Servers 6.1.6 UNIX, Sun, HP, and LINUX Origins
of UNIX
UNIX is the name of a group of operating
systems that trace their origins back to 1969 at Bell Labs.
Since its inception, UNIX was designed to support multiple
users and multitasking. UNIX was also one of the first
operating systems to include support for Internet networking
protocols. The history of UNIX, which now spans over 30 years,
is complicated because many companies and organizations have
contributed to its development. UNIX was first written in
assembly language, a primitive set of instructions that control
the internal instructions of a computer. However, UNIX could
only run on a specific type of computer. In 1971, Dennis
Ritchie created the C language. In 1973, Ritchie along with
fellow Bell Labs programmer Ken Thompson rewrote the UNIX
system programs in C language. Because C is a higher-level
language, UNIX could be moved or ported to another computer
with far less programming effort. The decision to develop this