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We can best define what a network is by describing what a network does. And then by analyzing some different types of networks that we are likely to come in contact with. So let's take a look at what a network does. First of all a computer network connects computers together for the purpose of sharing hardware, software, data and services. In other words a computer network allows more than one individual to use the same network resources, and this in effect saves a company a tremendous amount of money. But a network should also provide a means of securing each member or node of the network. In other words, information that should be shared should be able to be shared through the network. But information that should remain confidential should be secured through the network. Some networks are better at security than others. Let's take a look at some of the different types of networks. A Peer-to-Peer or Workgroup network is a combination of computers that are connected to each other or connected to each other through a hub. But each computer controls its own security, and there is no centralized security in a Peer-to-Peer or Workgroup type network. Each computer has it's own security accounts management database and controls who can get access to which resources. And each computer might also be processing information for other computers, since there are no servers in a Peer-to-Peer or workgroup type network. In contrast, a Server-Centric network provides a special type of computer called a Server to give resources to the network. And in addition provides clients that take information from the network. So in a Server-Centric network, we can have powerful workstations, since the workstations will only be processing what they individually process. And in fact, the Server can do some of the processing for the clients. So in a Server-Centric environment, we can use our resources in a much more efficient way. But we still have no centralized security; each network member or node controls it's own security. In a Domain, we have specific types of servers called Domain Controllers. And Domain Controllers are responsible for authenticating all of the nodes on to the network. In other words, you put in a username and a password to get into the network. If you do not have a username and a password, you don't get on to the network; the Domain Controller is responsible for who gets on to the network, and what resources they are allowed to have. The most sophisticated type of Domain is an Active Directory Domain. Windows 2000 and Novell servers use Active Directory. And in an Active Directory, everything that's on the network, whether it is a computer, a user, a printer (you name it) - everything is an object, and every object is fully controllable. Every object can be controlled as to what it can do to other objects, and what other objects can do to it. So the security can be extremely flexible and extremely granular in an Active Directory type of network. There are many training classes and other forms of training for Active Directory and for Domains, and I highly recommend that you take advantage of some of those. But we are going to focus in this training on Peer-to-Peer and Server-Centric. So since we have defined what these are, in our next section we will take a look at the environments that we would use a Peer-to-Peer network, and the environment that we would use a Server-Centric network. That's next.