Some computers handle the needs of many users at the same time. These powerful systems are most often used by organizations, such as businesses or schools, and are commonly found at the heart of the organization’s network.
Generally, each user interacts with the computer through his or her own device, freeing people from having to wait their turn at a single keyboard and monitor. The largest organizational computers support thousands of individual users at the same time, from thousands of miles away. While some of these large-scale systems are devoted to a special purpose, enabling users to perform only a few specific tasks, many organizational computers are general purpose systems that support a wide variety of tasks.
Today, most organizations’ networks are based on personal computers. Individual users have their own desktop computers, which are connected to one or more centralized computers, called network servers. A network server is usually a powerful personal computer with special software and equipment that enable it to function as the primary computer in the network. PC-based networks and servers offer companies a great deal of flexibility. For example, large organizations may have dozens or hundreds of individual servers working together at the heart of their network. When set up in such groups— sometimes called clusters or server farms—network servers may not even resemble standard PCs. For example, they may be mounted in large racks or reduced to small units called “blades," which can be slid in and out of a case. In these large networks, different groups of servers may have different purposes, such as supporting a certain set of users, handling printing tasks, enabling Internet communications, and so on.
A PC-based server gives users the flexibility to do different kinds of tasks. This is because PCs are general-purpose machines, designed to be used in many ways. For example, some users may rely on the server for e-mail access, some may use it to perform accounting tasks, and others may use it to perform word-processing or database management jobs. The server can support these processes, and many others, while storing information and programs for many people to use.
Depending on how the network is set up, users may be able to access the server in multiple ways. of course, most users have a standard desktop PC on their desk that is permanently connected to the network. Mobile users, however, may be able to connect a notebook PC or a handheld device to the network by wireless means. When they are away from the office, users may be able to use the Internet as a means of connecting to the company’s network servers.
Mainframe computers are used in large organizations such as insurance companies and banks, where many people frequently need to use the same data. In a traditional mainframe environment, each user accesses the mainframe’s resources through a device called a terminal. There are two kinds of terminals. A dumb terminal does not process or store data; it is simply an input/output (I/O) device that functions as a window into a computer located somewhere else.
An intelligent terminal can perform some processing operations, but it usually does not have any storage. In some mainframe environments, however, workers can use a standard personal computer to access the mainframe.
Mainframes are large, powerful systems. The largest mainframes can handle the processing needs of thousands of users at any given moment. But what these systems offer in power, they lack in flexibility. Most mainframe systems are designed to handle only a specific set of tasks. In your state's Department of Motor Vehicles, for example, a mainframe system is probably devoted to storing information about drivers, vehicles, and driver's licenses, but little or nothing else. By limiting the number of tasks the system must perform, administrators preserve as much power as possible for required operations.
First released in the 1960s, minicomputers got their name because of their small size compared to other computers of the day. The capabilities of a minicomputer are somewhere between those of mainframes and personal computers. For this reason, minicomputers are often called midrange computers. Like mainframes, minicomputers can handle much more input and output than personal computers can. Although some ‘‘minis’’ arc designed for a single user, the most powerful minicomputers can serve the input and output needs of hundreds of users at a time. Users can access a central minicomputer through a terminal or a standard PC.
Supercomputers are the most powerful computers made, and physically they are some of the largest. These systems can process huge amounts of data, and the fastest supercomputers can perform more than one trillion calculations per second. Some supercomputers can house thousands of processors. Supercomputers are ideal for handling large and highly complex problems that require extreme calculating power. For example, supercomputers have long been used in the mapping of the human genome, forecasting weather, and modeling complex processes like nuclear fission.