Servers are computers just like any other, but usually far more powerful.

Once again there will be an Operating System (e.g. Microsoft Windows Server, Mac OS X Server, Solaris etc) and this can be enough to provide network services to client machines (authentication, internet access, storage space etc).

But often server applications (e.g. Microsoft Exchange, SQL) are installed as well to provide further services to the client machines (email, databases etc).

Usually you require licences for the Operating System (e.g. Microsoft) and the applications that are installed or made available to users.

You usually also require licences for the clients to connect to the server and receive the services (e.g. Microsoft Windows CAL's)

NB - Sometimes you will have a choice as to whether you combine the connection to server licences into the server licensing itself (processor licences).  This can get complicated both from a technical perspective and from the quantity of choices that is available.

It is worth making sure you have a good understanding of this area however, as the financial risks can be huge.

An example
So if you are running a Microsoft server with Exchange installed that is providing email to 250 client machines (or users) you will require the following licences:
  • Windows Server licence x 1
  • Exchange Server licence x 1
  • Windows CAL licences x 250 (that matches the version of the server licence e.g. 2003)
  • Exchange CAL licences x 250 (that matches the version of the Exchange server licence e.g. 2003)

We now go into more detail around Connections to servers...