Mid-Range Power: The Evolution of ClientServer Computing

Mid-Range Power: The Evolution of Client/Server Computing

Until the mid-1980s, almost all computing was done on a mainframe or a minicomputer that acted as a host for a number of users connected by a terminal. The advent of the PC allowed users to perform certain tasks on their PCs that did not require the resources of a host computer. Any files that needed to be transferred between the two were sent and received by file transfer routines. A typical example was the transfer of a DOS PC data file to a UNIX host for processing on the UNIX host.

The arrival of the mid-range computer allowed a wider range of services to a connected PC than the mainframe. The mid-range computer could perform some of the tasks that were considered too small for the mainframe but were, in most cases, too complex for the PC. Such a computer was called a server, because it “served” things to PCs that were connected to it, such as common files or programs. The UNIX operating system, which had previously run only on larger computers, was resized to keep all of its important features and run on much smaller systems such as mid-range computers and workstations.

Coincident with this was the introduction of the local area network, or LAN. This networking architecture allowed users in the same workgroup to share applications and data with each other, as well as to share resources such as printers and files. In addition to connecting PCs together, LANs made it possible for PCs to act as clients, or devices that ask for some type of service, from a mid-range machine acting as a server on the network. This also allowed the mid-range machines to act as communications servers for such things as faxing and access to other network services such as the Internet. The combination of these new environments led to the introduction of a new way of computing, called client/server computing.

UNIX has turned out to be a highly suitable server operating system. It has the robustness to provide services to many types of clients with different operating systems such as Windows and Macintosh. At the same time it can provide linkages to mainframes in large data centers. UNIX is also useful as a client operating system, especially on workstations. For a more detailed discussion of the range of capabilities of UNIX, refer to Chapter 1.