Computer Systems
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- Classification according to the purpose General purpose
- Classification according to the technology Analog Computers
- Classification according to the size/performance Micro Computers
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Computer Systems A complete, working computer is referred to as a computer system. Computer systems will include the computer along with any software and peripheral devices that are necessary to make the computer function. A computer system is consists of Hardware, Software, Firmware and Liveware. Conventionally, a computer 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. Peripheral devices allow information to be retrieved from an external source, and the result of operations saved and retrieved. 
Hardware The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware. Computer hardware is the collection of physical elements that constitutes a computer system. A combination of hardware and software forms a usable computing system. Software 
Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified. The term is generic, in that it refers to all computer programs regardless of their architecture; for example, executable files, libraries and scripts are computer software. Yet, it shares their mutual properties: software consists of clearly-defined instructions that upon execution, instructs hardware to perform the tasks for which it is designed. On virtually all computer platforms, software can be grouped into a few broad categories. Application software uses the computer system to perform useful work or provide entertainment functions beyond the basic operation of the computer itself. The term is used to contrast such software with system software, which manages and integrates a computer& capabilities but does not directly perform tasks that benefit the user. The system software serves the application, which in turn serves the user. Examples include accounting software, enterprise software, graphics software, media players, and office suites. Many application programs deal principally with documents. Applications may be bundled with the computer and its system software or published separately, and can be coded as university projects. System software is designed to operate the computer hardware, to provide basic functionality, and to provide a platform for running application software. The operating system (prominent examples being z/OS, Microsoft Windows, Mac OS X and Linux), allows the parts of a computer to work together by performing tasks like transferring data between memory and disks or rendering output onto a display device. It also provides a platform to run high-level system software and application software. 
Utility software helps to analyze, configure, optimize and maintain the computer. Device drivers such as computer BIOS and device firmware provide basic functionality to operate and control the hardware connected to or built into the computer. A user interface & allows users to interact with a computer. Since the 1980s the graphical user interface (GUI) has been perhaps the most common user interface technology. The command-line interface is still a commonly used alternative. Malicious software or malware, computer software developed to harm and disrupt computers. As such, malware is undesirable. Malware is closely associated with computer-related crimes, Firmware Permanent software programmed into a read-only memory. In electronic systems and computing, firmware is the combination of persistent memory and program code and data stored in it. Typical examples of devices containing firmware are embedded systems (such as traffic lights, consumer appliances, and digital watches), computers, computer peripherals, mobile phones, and digital cameras. The firmware contained in these devices provides the control program for the device. Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory. Liveware Working personnel, especially computer personnel, as distinct from the inanimate or abstract things they work with. Thought of as a component of the system along with hardware and software. Classification according to the purpose General purpose: A general purpose computer as the name suggests is a computer that has capabilities to perform a wide range of tasks. It performs with reasonable degrees efficiency both scientific and business applications. The opposites of general purpose computers are dedicated computers which are usually specialized in performing one given role to utmost efficiency. General-purpose computers are designed to solve a large variety of problems. That is they can be given different programs to solve different types of problems. General-purpose computers can process business data as readily as they process complex mathematical formulas. General-purpose computers can store large amount of data and the programs necessary to process them. Because general- purpose computers are so versatile, most businesses today use them. Most digital computers are general computers and it is mainly such computers that are used in business and commercial data processing. Specific purpose: Special purpose computers are designed to solve a specific problems; the computer program for solving the problem is built right into the computer. Special purpose computers have many features of general-purpose computers but are designed to handle specific problems and are not applied to other computerized activities. For example, special purpose computers may be designed to process only numeric data or to completely control automated manufacturing processes. Moat analogue computers are special purpose computers. Special purpose computers are often used as training simulators. A simulator is a computer-controlled device for training people under simulated, or artificially created, conditions. The computer creates test conditions the trainee must respond. It then records and evaluates he responses, providing these results to both trainee and supervisor. Classification according to the technology Analog Computers: An analog computer is a form of computer that uses the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. In contrast, digital computers represent varying quantities symbolically, as their numerical values change. As an analog computer does not use discrete values, but rather continuous values, processes cannot be reliably repeated with exact equivalence, as they can with Turing machines. Analog computers were widely used in scientific and industrial applications where digital computers of the time lacked sufficient performance. Analog computers can have a very wide range of complexity. Slide rules and monographs are the simplest, while naval gunfire control computers and large hybrid digital/analog computers were among the most complicated. Systems for process control and protective relays used analog computation to perform control and protective functions. Digital Computers: Any of a class of devices capable of solving problems by processing information in discrete form. It operates on data, including magnitudes, letters, and symbols, that are expressed in binary form—i.e., using only the two digits 0 and 1. By counting, comparing, and manipulating these digits or their combinations according to a set of instructions held in its memory, a digital computer can perform such tasks as to control industrial processes and regulate the operations of machines. Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space. Simple computers are small enough to fit into mobile devices, and mobile computers can be powered by small batteries. Personal computers in their various forms are icons of the Information Age and are what most people think of as “computers.” However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are the most numerous. Hybrid Computers: Hybrid computers are computers that exhibit features of analog computers and digital computers. The digital component normally serves as the controller and provides logical operations, while the analog component normally serves as a solver of differential equations. Hybrid computers can be used to obtain a very good but relatively imprecise; value, using an analog computer front-end, which is then fed into a digital computer iterative process to achieve the final desired degree of precision. With a three or four digit, highly accurate numerical seed, the total digital computation time necessary to reach the desired precision is dramatically reduced, since many fewer iterations are required. One of the main technical problems to be overcome in hybrid computers is minimizing digital- computer noise in analog computing elements and ground systems. Hybrid computers should be distinguished from hybrid systems. The latter may be no more than a digital computer equipped with an analog-to- digital converter at the input and/or a digital-to- analog converter at the output, to convert analog signals for ordinary digital signal processing, and conversely, e.g., for driving physical control systems, such as servomechanisms. Classification according to the size/performance Micro Computers: A microcomputer is a small, relatively inexpensive computer with a microprocessor as its central processing unit (CPU). It includes a microprocessor, memory, and input/output (I/O) facilities. Microcomputers became popular in the 1970s and 80s with the advent of increasingly powerful microprocessors. The predecessors to these computers, mainframes and minicomputers, were comparatively much larger and more expensive (though indeed present-day mainframes such as the IBM System z machines use one or more custom microprocessors as their CPUs). Many microcomputers (when equipped with a keyboard and screen for input and output) are also personal computers. 
Mini Computers: A minicomputer, or colloquially mini, is a class of smaller computers that evolved in the mid-1960s and sold for much less than mainframe and mid- size computers from IBM and its direct competitors. In size and power, minicomputers lie between workstations and mainframes. In the past decade, the distinction between large minicomputers and small mainframes has blurred, however, as has the distinction between small minicomputers and workstations. But in general, a minicomputer is a multiprocessing system capable of supporting from 4 to about 200 users simultaneously. Typically, minicomputers have been stand-alone computers (computer systems with attached terminals and other devices) sold to small and mid-size businesses for general business applications and to large enterprises for department-level operations. In recent years, the minicomputer has evolved into the mid-range server; and is part of a network. 
Mainframe Computers: Mainframe computers (colloquially referred to as big Iron) are computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning and transaction processing. The term originally referred to the large cabinets called “main frames” that housed the central processing unit and main memory of early computers. A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation. Supercomputers are used for scientific and engineering problems (high-performance computing) which are data crunching and number crunching, while mainframes are used for transaction processing. Modern mainframes can run multiple different instances of operating systems at the same time. This technique of virtual machines allows applications to run as if they were on physically distinct computers. In this role, a single mainframe can replace higher-functioning hardware services available to conventional servers. While mainframes pioneered this capability, virtualization is now available on most families of computer systems, though not always to the same degree or level of sophistication. 
Super Computers: A supercomputer is a computer at the frontline of contemporary processing capacity – particularly speed of calculation. Supercomputers play an important role in the field of computational science, and are used for a wide range of intensive tasks in various fields, including quantum mechanics, weather forecasting, climate research, oil and gas exploration, molecular modeling (computing the structures and properties of chemical compounds, biological macromolecules, polymers, and crystals), and physical simulations (such as simulations of the early moments of the universe, airplane and spacecraft aerodynamics, the detonation of nuclear weapons, and nuclear fusion). Throughout their history, they have been essential in the field of cryptanalysis. The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently. 
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