The network is one of the major backbones for a company’s computer system.  As companies grow, the network is one of the easiest things to forget about.  It is hidden in the back closet and rarely gets seen, yet it is one of the first things that can cause speed issues.  This usually occurs because of an older style switch with multiple computers using it.  A bottle neck happens in the output of the switch to the router or another switch.  If the output is only 100 Mbs and you have 5 computers on it, they are sharing this 100 Mbs and not always evenly.  The more computers you add, the slower it can get, occasionally leaving 1 or 2 computers with almost none.  With newer equipment and network planning, these bottle necks can be almost eliminated.