A computer is a device that accepts information and manipulates it for some result based on a program or sequence of instructions on how the data to be processed. Basically, there are four types of computer namely supercomputer, mainframe, mini computer, and microcomputer.
SUPERCOMPUTER
A supercomputer is the fastest type of computer which performs at or near the currently highest operational rate for computers. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations, handle very large database or do a great amount of computation. For example, weather and global climate forecasting requires a supercomputer. Other uses of supercomputers include animated graphics, fluid dynamic calculations, nuclear energy research, petroleum exploration, design automobiles, aircraft and spacecraft, design new drugs and chemical compounds; and to make calculations that help scientists understand the properties of particles that make up atoms as well as the behavior and evolution of stars and galaxies. Supercomputers are also used extensively by the military for weapons and defense systems research, and for encrypting and decoding sensitive intelligence information. Supercomputers introduced in the 1960s were designed primarily by Seymour Cray at Control Data Corporation (CDC), and led the market into the 1970s until Cray left to form his own company, Cray Research. He then took over the supercomputer market with his new designs, holding the top spot in supercomputing for five years which is from 1985 to 1990. Cray, himself, never used the word "supercomputer"; a little-remembered fact is that he only recognized the word "computer". In the 1980s a large number of smaller competitors entered the market, in a parallel to the creation of the minicomputer market a decade earlier, but many of these disappeared in the mid-1990s "supercomputer market crash". Today, supercomputers are typically one-of-a-kind custom designs produced by "traditional" companies such as Cray, IBM and HP, who had purchased many of the 1980s companies to gain their experience. Supercomputers are different from other types of computers in that they are designed to work on a single problem at a time, devoting all their resources to the solution of the problem. Other powerful computers such as mainframes and workstations are specifically designed so that they can work on numerous problems, and support numerous users, simultaneously. Because of their high cost—usually in the hundreds of thousands to millions of dollars—supercomputers are shared resources. Supercomputers are so expensive that usually only large companies, universities, government agencies and laboratories that can afford them. The two major components of a supercomputer are the same as any other computer—a central processing unit (CPU) where instructions are carried out, and the memory in which data and instructions are stored. The CPU in a supercomputer is similar in function to a standard personal computer (PC) CPU, but it usually has a different type of transistor technology that minimizes transistor switching time. Switching time is the length of time that it takes for a transistor in the CPU to open or close, which corresponds to a piece of data moving or changing value in the computer. This time is extremely important in determining the absolute speed at which a CPU can operate. By using very high performance circuits, architectures, and, in some cases, even special materials, supercomputer designers are able to make CPUs that are 10 to 20 times faster than state-of-the-art processors for other types of commercial computers. Supercomputer memory also has the same function as memory in other computers, but it is optimized so that retrieval of data and instructions from memory takes the least amount of time possible. Also important to supercomputer performance is that the connections between the memory and the CPU be as short as possible to minimize the time that information takes to travel between the memory and the CPU.
MAINFRAME
A mainframe which is often colloquially known as "big iron" is a high-performance computer used for large-scale computing purposes that require greater availability and security than a smaller-scale machine can offer. It is a very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simple microprocessor (in watches, for example) at the bottom and moves to supercomputers at the top, mainframes are just below supercomputers. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. However, supercomputers can execute a single program faster than a mainframe. It is used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, ERP, and financial transaction processing. The mainframe is sometimes referred to as a "dinosaur" not only because of its size but because of reports, going back many years, that it's becoming extinct. In 1991 Stewart Alsop, the editor of InfoWorld, predicted that the last mainframe would be retired by 1996. However, in February 2008 IBM released a new mainframe, the z10. Steve Lohr wrote about the mainframe as "the classic survivor technology" in The New York Times ("Why old technologies are still kicking"): I.B.M. overhauled the insides of the mainframe, using low-cost microprocessors as the computing engine. The company invested and updated the mainframe software, so that banks, corporations and government agencies could still rely on the mainframe as the rock-solid reliable and secure computer for vital transactions and data, while allowing it to take on new chores like running Web-based programs. The original mainframes were housed in room-sized metal frames, which is probably where the name derives from. In the past, a typical mainframe might have occupied 2,000 - 10,000 square feet. Newer mainframes are about the same size as a large refrigerator.
MICROCOMPUTER
Microcomputer, is a desktop or notebook-size computing device that uses a microprocessor as its central processing unit, or CPU. In common usage, the term microcomputer is equivalent to personal computer or PC. Microcomputers are designed to be used by individuals, whether in the form of PCs, workstations or notebook computers. A microcomputer contains a central processing unit (CPU) on a microchip (the microprocessor), a memory system (typically read-only memory and random access memory), a bus system and I/O ports, typically housed in a motherboard. When they first appeared, microcomputers were considered single-user devices, and they were capable of handling only 4, 8, or 16 bits of information at one time. Over time the distinction between microcomputers and large, mainframe computers (as well as the smaller mainframe-type systems called minicomputers) has become blurred, as newer microcomputer models have increased the speed and data-handling capabilities of their CPUs into the 32-bit and 64-bit, multiuser range.
MINICOMPUTER
A minicomputer, a term no longer much used, is a computer of a size intermediate between a microcomputer and a mainframe. In times past, the minicomputer was typically a stand alone device that was ideal for use by small and mid-sized businesses who needed more power and memory than could be obtained with microcomputers, but did not have a need for the resources provided by mainframes. More recently, a minicomputer is thought of in terms of being a server that is part of a larger network. In the early years of computer technology, a hierarchy of computer sizes and types was used to define the level of operation needed for different types of applications. The levels ranged from the embedded systems that functioned more or less automatically to parallel processing systems that was capable of supporting a huge network of interconnected computers and performing a wide array of tasks simultaneously. The minicomputer tended to be somewhat low on the hierarchical listing, in that the device was considered to be limited in ability. The original structure for a minicomputer was a simple computer system that was equipped with essential programs and functions that would handle simple tasks, such as word processing. The minicomputer was equipped with terminals that made it possible to attach peripheral devices to the system, such as a printer. However, the minicomputer usually did not have hardware or software that allowed the device to be integrated into a larger network. However, if there was no need to use comprehensive applications or interact with other systems, the minicomputer was often sufficient. Over time, the concept of a minicomputer has become somewhat obsolete. As technology has continued to evolve, many tasks that were once the exclusive province of the larger and more powerful mainframe computers has been assumed by the workstation computers of today. Still, the mainframe remains in existence, although the purpose and function is often associated with the role of a large server to support a network of workstations. In like manner, the minicomputer has morphed into a server that is ideal for smaller and more localized networks.
