As time passed, the size of networks increased, the demands for speed increased, and classic client/server model evolved. Under a peer-to-peer model, each node on the network has the potential to borrow or share resources located on another node. This model could not survive in an increasingly large and complex networked environment. It became necessary to design a network model that could accommodate the need for security, centralized control, and ease of growth. The client/server model, which somewhat differs from the fashionable use of this term today, originally provided for a central system providing services that could be used by authorized clients on the network.

As the server concept evolved, there was an increased recognition of the special computing demands made on a server, as opposed to a general purpose workstation. A file server is extremely I/O intensive, which implies optimizing the ability of the server to handle large amounts of traffic to and from the network, as well as frequent, sizable data transfers to and from its storage subsystem. These considerations have influenced the evolution of server and server subsystem design.

As the overall size and complexity of networks has increased, the need to structure, segment and control the physical and logical layout of the network has led to the development of such networking devices as bridges, routers and hubs. The need to connect dissimilar networks together has produced such components as multi-protocol routers, translation bridges, and gateways.

Wide-area networks, which extend the reach of the network across large geographic areas, have required the connection of the local networks to public carrier services. The earliest and most common being the telephone system. Voice grade lines could be utilized with analog modems, which transmit data in a form compatible with voice transmission. Higher speed and greater reliability are achieved by using high speed data-grade lines, with names such as 56kb, T-1, and T-3 lines. These can be leased from the telephone company or private carriers, and require the use of digital modems, called CSU/DSUs to achieve high rates of data transfer. In addition, there are public data networks, such as X.25, that can be accessed using wide-area gateways.

These various devices will be covered in greater detail in the sections that follow.