A server is any computer that performs network functions for other computers. These
functions fall into several categories, including the following:
File and print servers, which provide file sharing and services to share
Application servers, which provide specific application services to an application.
An example is a server that runs a database that a distributed application uses.
E-mail servers, which provide e-mail storage and interconnection services to
Networking servers, which can provide a host of different network services.
Examples of these services include the automatic assignment of TCP/IP addresses
(DHCP servers), routing of packets from one network to another (routing servers),
encryption/decryption and other security services, and VPN access.
Internet servers, which provide Web, Usenet News (NNTP), and Internet
Remote access servers, which provide access to a local network for remote users.
As noted earlier, servers typically run some sort of network operating system, such
as Windows Server 2008, Linux, or UNIX. Depending on the operating system chosen,
the functions previously listed might all be performed on one server or distributed to
many servers. Also, not all networks need all the services previously listed.
Server computers can be nearly any type of computer, but today they are usually high-end
Intel-based PCs. You might also see certain types of servers that use a different platform.
For instance, many dedicated web servers run on UNIX-based computers, such as those from
Sun Microsystems, IBM, Hewlett-Packard, and other vendors.
A number of features distinguish a true server-class computer from a more
pedestrian client computer, including the following:
Built-in redundancy with multiple power supplies and fans (for instance) to
keep the server running if something breaks.
Special high-performance designs for disk subsystems, memory, and network
subsystems to optimize the movement of data to and from the server, the
network, and the client computers.
Special monitoring software and hardware that keeps a close watch on the
health of the server, warning of failures before they occur. For example, most
servers have temperature monitors; if the temperature starts getting too high,
a warning is issued so the problem can be resolved before it causes failure of
any of the hardware components in the server.
You can learn more about servers in Chapter 13.