A computer is a programmable machine. It accepts information in the form of digitized data and manipulates it for some result based on a program or sequence of instructions on how the data is to be processed. It consists of at least one processing element, typically a central processing unit (CPU) and some form of memory. The processing element carries out arithmetic and logic operations, and a sequencing and control unit that can change the order of operations based on stored information.
Computers are also categorized on the basis of physical structures and the purpose of their use. Based on Capacity, speed and reliability they can be divided following categories of computers:
1. Microcomputer Systems
Microcomputers are the most important category of computer systems for end users. Though usually called a personal computer, or PC, a microcomputer is much more than a small computer for use by an individual. The computing power of microcomputers now exceeds that of the mainframes of previous computer generations at a fraction of their cost. Thus, they have become powerful networked professional work stations for end users in business.
Microcomputers come in a variety of sizes and shapes for a variety of purposes. For example, PCs are available as handhled, notebook, laptop, portable, desktop, and floor-standing models. Or, based on their use, they include home, personal, professional, workstation, and multi-user systems. Most microcomputers are desktops designed to fit on an office desk, or notebooks for those who want a small, portable PC for their work activities.
Some microcomputers are powerful workstation computers (technical work-stations) that support applications with heavy mathematical computing and graphics display demands such as computer-aided design (CAD) in engineering, or investment and portfolio analysis in the securities industry. Other microcomputers are used as network servers. They are usually more powerful microcomputers that coordinate telecommunications and resource sharing in small local area networks (LANs), and Internet and intranet Web sites. Another important microcomputer category includes handheld microcomputer devices known as personal digital assistants (PDAs), designed for convenient mobile communications and computing. PDAs use touch-screens, pen-based handwriting recognition of keyboards to help mobile workers send and receive E-mail and exchange information such as appointments, to do lists, and scales contacts with their desktop PCs or Web servers.
2. Multimedia Computer Systems
Multimedia PCs are designed to present you with information in a variety of media, including text and graphics displays, voice and other digitized audio, photographs, animation, and video clips. Mention multimedia, many people think of computer video games, multimedia encyclopedias, educational videos, and multimedia home pages on the World Wide Web. However, multimedia systems are widely used in business for training employees, educating customers, making sales presentations, and adding impact to other business presentations.
The basic hardware and software requirements of a multimedia computer system depend on whether you wish to create as well as enjoy multimedia presentations. Owners of low-cost multimedia PCs marketed for home used do not need authoring software or high-powered hardware capacities in order to enjoy multimedia games and other entertainment and educational multimedia products. These computers come equipped with a CD-ROM drive, stereo speakers, additional memory, a high-performance processor, and other multimedia processing capabilities.
People who want to create their own multimedia production may have to spend several thousand dollars to put together a high-performance multimedia authoring system. This includes a high-resolution color graphics monitor, sound and video capture boards, a high-performance microprocessor with multimedia capabilities, additional megabytes of memory, and several gigabytes of hard disk capacity. Sound cards and video capture boards are circuit boards that contain digital signal processors (DSPs) and additional megabytes of memory for digital processing of sound and video. A digital camera, digital video camcorder, optical scanner, and software such as authoring tools and programs for image editing and graphics creation can add several thousand dollars to the star-up costs of a multimedia authoring system.
3. Midrange Computer Systems
Midrange Computers, including minicomputers and high-end network servers, are multi-user systems that can manage network of PCs and terminals. Though not as powerful as mainframe computers, they are less costly to buy, operate, and maintain than mainframe systems, and thus meet the computing needs of many organizations.
Midrange computers first became popular as minicomputers for scientific research, instrumentation systems, and industrial process monitoring and control. Minicomputers could easily handle such uses because these applications are narrow in scope and do not demand the processing versatility of mainframe systems. Thus, midrange computers serve as industrial process-control and manufacturing plant computers, and they still play a major role in computer-aided manufacturing (CAM). They can also take the form of powerful technical workstations for computer-aided design (CAD) and other computation and graphics-intensive applications. Midrange computers are also used as front-end computers to assist mainframe computers in telecommunication processing and network management.
Midrange computers have become popular as powerful network servers to help manage large Internet Web sites, corporate intranets and extranets, and client/server networks. Electronic commerce and other business uses of the Internet are popular high-end server applications, as are integrated enterprise wide manufacturing, distribution and financial applications. Other applications, like data warehouse management, data mining, and online analytical processing.
4. Mainframe Computer Systems
Mainframe computes are large, fast, and powerful computer systems. For example, mainframes can process hundreds of million instructions per second (MIPS). Mainframes also have large primary storage capacities. Their main memory capacity can range from hundreds of megabytes to many gigabytes of primary storage. And mainframes have slimmed down drastically in the last few years, dramatically reducing their air-conditioning needs, electrical power consumption, and floor space requirements, and thus their acquisition and operating costs. Most of these improvements are the result of a move from water-cooled mainframes to a new CMOS air-cooled technology for mainframe systems.
Thus, mainframe computers continue to handle the information processing needs of major corporations and government agencies with many employees and customers or with complex computational problems. For example, major international banks, airlines, oil companies, and other large corporations process millions of sales transactions and customer inquiries each day with the help of large mainframe systems. Mainframes are still used for computation-intensive applications such as analyzing seismic data from oil field explorations or simulating flight conditions in designing aircraft. Mainframes are also widely used as super server for the large client/server network and high-volume Internet Web sites of large companies.
5. Supercomputer Systems
The term supercomputer describes a category of extremely powerful computer systems specifically designed for scientific, engineering, and business applications requiring extremely high speeds for massive numeric computations. The market for supercomputers includes government research agencies, large universities, and major corporations. They use supercomputers for applications such as global weather forecasting, military defense systems, computational cosmology and astronomy, microprocessor research and design, large-scale data mining and so on.
Supercomputers use parallel processing architectures of interconnected microprocessors (which can execute many instructions at the same time in parallel). They can perform arithmetic calculations at speeds of billions of floating-point operations per second (gigaflops). Teraflop (1 trillion floating-point operations per second) supercomputers, which use advanced massively parallel processing (MPP) designs of thousands of interconnected microprocessors, are becoming available. Purchase prices for large supercomputers are in the $5 million to $50 million range.
However, the use of symmetric multiprocessing (SMP) and distributed shared memory (DSM) designs of smaller numbers of interconnected microprocessors has spawned a breed of minisuper computers with prices that start in the hundreds of thousands of dollars.