In some networks, a server computer is a server computer and nothing else.
It’s dedicated to the sole task of providing shared resources, such as hard
drives and printers, to be accessed by the network client computers. Such a
server is referred to as a dedicated server because it can perform no other
task besides network services.

Other networks take an alternative approach, enabling any computer on the
network to function as both a client and a server. Thus, any computer can
share its printers and hard drives with other computers on the network. And
while a computer is working as a server, you can still use that same computer
for other functions such as word processing. This type of network is called
a peer-to-peer network, because all the computers are thought of as peers,
or equals.

The network computer that contains the hard drives, printers, and other
resources that are shared with other network computers is called a server.
This term comes up repeatedly, so you have to remember it. Write it on the
back of your left hand.

Any computer that’s not a server is called a client. You have to remember this
term, too. Write it on the back of your right hand.
Only two kinds of computers are on a network: servers and clients. Look at
your left hand and then look at your right hand. Don’t wash your hands until
you have these terms memorized.
The distinction between servers and clients in a network has parallels in
sociology — in effect, a sort of class distinction between the “haves” and
“have-nots” of computer resources:
 Usually, the most powerful and expensive computers in a network are
the servers. There’s a good technical reason: Every user on the network
shares the server’s resources.
 The cheaper and less powerful computers in a network are the clients.
Clients are the computers used by individual users for everyday work.
Because clients’ resources don’t have to be shared, they don’t have to
be as fancy.
 Most networks have more clients than servers. For example, a network
with ten clients can probably get by with one server.
 In many networks, a clean line of demarcation exists between servers
and clients. In other words, a computer functions as either a server or a
client, and not both. For the sake of an efficient network, a server can’t
become a client, nor can a client become a server.
 Other (usually smaller) networks can be more even-handed, allowing
any computer in the network to be a server and client at the same time.

A network is nothing more than two or more computers connected by a
cable (or in some cases, by a wireless connection) so that they can exchange
information.
Of course, computers can exchange information in other ways besides networks.
Most of us have used what computer nerds call the sneakernet. That’s
where you copy a file to a diskette and then walk the disk over to someone
else’s computer. (The term sneakernet is typical of computer nerds’ feeble
attempts at humor, and why not? As a way to transfer information, sneakernet
was pretty feeble.)