Desktop computer
Classification according to the logic used
Analog Computers:
These computers recognize data as a continuous measurement of a physical property. Their output is usually in the form of readings on dials or graphs. Voltage, pressure, speed and temperatures are some physical properties that can be measured in this way. For e.g.
1. A Service Station gasoline pump contains an analog processor that connects fuel flow measurements into quantity and price values.
2. Automobile speedometer, etc
Digital Computers:
These are high-speed programmable computer devices that perform mathematical calculations, compare values, and store the results. They recognize data by counting discrete signals representing either a high (?on?) or low (?off?) voltage state of electricity. Numbers, alphabets and special symbols can all be reduced to representation by 1s and 0s. For e.g.
Personal computers
Scoreboard that directly counts discrete values such as the time left to play and the score of each team.
Digital computers are further grouped into two categories:
General-purpose digital computers: The digital computers, which can theoretically be used for any type of application, are called general-purpose digital computers. For e.g. the computers that are used for payroll, graphs, analysis, account, banking system, etc.
Special purpose digital computers: These are those digital computers, which are made and used for a specific job. For e.g. the computer installed in automobiles to control ignition instrument and braking systems.
Hybrid Computers:
Hybrid computers combine the best features of analog and digital computers. They have the speed of analog computers and the accuracy of digital computers. They are usually used for special problems in which input data derived from measurements is converted into digits and processed by computer. Consider the hybrid computer used in producing iron ore pellets for steel making. It controls manufacturing and prepares production data on inventory and costs. The computer accepts data both from sensors within the production area and from conventional Input/Output (I/O) devices.
As production starts, data on the materials used in manufacturing goes into the computer for analysis. The computer uses the data to establish operating standards. Sensors report on all aspects of manufacturing and the computer converts these measurements into numeric equivalents. The computer ensures that all operations are within limits and quickly notes exceptions.
Using the production data, the computer plans for future manufacturing and distributes existing inventories; activities, which require the computer to compute digital data and, produce reports for management. The hybrid computer is perfectly suited to this application. The computer can act like an analog computer, converting measurements into numeric input. It can act as a digital computer, processing stored data for management.
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Classification according to size
There are both large and small computers.
Large Computer Systems:
They have been traditionally divided into three main categories:
1. Super Computers: A super computer is generally characterized as being the fastest, most powerful and most expensive computer. One of the most powerful super computers today, the Cray-2 is set up in a C-shape, is not as tall as a person and is small enough to fit in the space of a large business desk. Supercomputers have large memories and high processing speeds; they can process up to billion instructions per second. They are used for processing very large files and performing large-scale mathematical calculations. In fact, supercomputers are used for such intense computing that they are enclosed in frames containing liquid coolant to prevent them from melting down.
Most supercomputers have two characteristics in common. One is the ability to recover automatically from failures. Also, unlike conventional computers, which have a single processor which processes one instruction at a time, supercomputers have multiple processors (or CPUs) that process multiple instructions at a time; this is known as parallel processing. Some applications to which parallel processing are ideally suited are resource optimization, image processing, graphics, and financial portfolio analysis.
Fault-tolerant computer use a backup mechanism to automatically isolate and reconfigure hardware that fails during system operation. Companies that require highly reliable computer systems use fault-tolerant computers. For e.g. European bank use fault-tolerant systems because of their reliability and their ability to process huge volumes of data. In the US, the Securities and Exchange Commission also uses fault-tolerant computers to analyze massive amounts of financial data that US Corporations submit to the commission. The White House has recently installed four high-security fault-tolerant computers for a wide variety of applications.
Supercomputers are widely used in scientific applications such as aerodynamic design and simulation, processing of geological data, processing of data regarding genetic coding and collecting and processing weather data.
2. Mainframe Computers: A mainframe computer is usually slower, less powerful and less expensive than supercomputers. Mainframes process data at several million instructions per second (MIPS). More than 1,000 remote workstations can be accommodated by a typical mainframe computer.
A technique that allows many people at terminals to access the same computer at one time is called time-sharing. Mainframes are used by banks and many businesses to update inventory, etc.
3. Minicomputer: Minicomputers are smaller than mainframe, general purpose computers, and give computing power without adding the prohibitive expenses associated with larger systems. The minicomputer?s size prevents it from being portable but it can be moved from easily than a mainframe.
Minicomputer integrates commercial and technical operations better than the more powerful computers. It is generally easier to use. Minicomputers are well adapted for functions such as accounting, word processing, database management, statistical packages for social sciences, Computer Aided Design (CAD) and Numerical Analysis, etc.
Small Computer Systems:
They have been divided into four categories:
(a) Microcomputers: A microcomputer is the smallest, least expensive of all the computers. The prefix ?micro? refers mainly to the physical size of the computer and its circuitry, rather than its capabilities.
The essential differences between microcomputers and mainframe or minicomputers are that microcomputers have smallest memory and less power, are physically smaller and permit fewer peripherals to be attached. Microcomputers are also called personal computers.
(b) Laptops and Notebooks: Laptops & notebooks provide mobile computing technology. These computers are battery-operated and hence can be used any time and anywhere. Laptop computers are small enough to fit on the lap of a user; notebook computers are even smaller. The primary differences between a laptop and a notebook are size and weight. Notebooks are smaller than laptops and weigh less. However, both are equipped with powerful microprocessors, graphic capabilities, adequate memory size, and mouse-driven input. Some laptops and notebooks even have false capabilities. CD-ROM drives, and optical storage devices and can be linked to various input and output devices.
(c) Hand-Held Computers: Hand-held computers are even smaller than notebooks. They are primarily used to collect field data. For e.g. archaeologists at a dig site in Jordan us hand-held computers to gather information about centuries-old artifacts. The New York City transit police use hand-held computers to apprehend criminals, when a suspect is apprehended, a police office uses a hand-held computer to do a background check on the individual. Each hand-held computer holds more than 1,200 records and provides police officers with timely and sometimes life-saving information.
(iv) Pen-Based Computing: Pen-based computing refers to portable computers that use an electronic writing pad and a light-sensitive electronic pen, thus freeing users from the constraints of a keyboard. When the user writes on the pad, the writing is converted into digital input and stored in a file in the computer. Pen-based computing is becoming increasingly popular because most people are comfortable using a pen. It is particularly useful for sales and service representatives, insurance agents, retail suppliers, delivery people, inventory clerks, and health care providers, who are often on the move.