Computer Education Chapter No 2

Definition

Computer is a device, which is capable of performing a series of arithmetic or logical operations. It can perform complexity of the operations, and has ability to process, store, and retrieve data without human intervention. Actually computers developed along with two separate engineering paths, producing two distinct types of computer Analog and Digital. Then with the combination of Digital and Analog an other type of computer developed called Hybrid Computer. These are three distinct families of computing device available to us today. These three types of computer operate on quite different principles mentioned as under:

Digital Computer

The digital computer is a sequential device, in general, operating on data one step at a time, using form of representation called binary. Thus a single transistor in a digital computer can only store two states, on and off. Obviously to store a number to any sensible degree of precision, many transistors are required.The advance technology of integrated circuits has the development of smaller and more powerful general-purpose digital computers. It has not only reduced the size of the large, multi-user mainframe computers, but also made possible powerful, single-user personal computers and workstations that can sit on a desktop.A digital computer is designed to process data in numerical form; its circuits perform directly the mathematical operations of addition, subtraction, multiplication, and division. The numbers operated on by a digital computer are expressed in the binary system; binary digits, or bits, are 0 and 1, so that 0, 1, 10, 11, 100, 101, etc., correspond to 0, 1, 2, 3, 4, 5, etc. Binary digits are easily expressed in the computer circuitry by the presence (1) or absence (0) of a current or voltage. A series of eight consecutive bits is called a “byte”; the eight-bit byte permits 256 different “on-off” combinations. Each byte can thus represent one of up to 256 alphanumeric characters, and such an arrangement is called a “single-byte character set” (SBCS); the de facto standard for this representation is the extended ASCII character set. Some languages, such as Japanese, Chinese, and Korean, require more than 256 unique symbols. The use of two bytes, or 16 bits, for each symbol, however, permits the representation of up to 65,536 characters or ideographs. Such an arrangement is called a “double-byte character set” (DBCS); Unicode is the international standard for such a character set. One or more bytes, depending on the computer's architecture, is sometimes called a digital word; it may specify not only the magnitude of the number in question, but also its sign (positive or negative), and may also contain redundant bits that allow automatic detection, and in some cases correction, of certain errors. A digital computer can store the results of its calculations for later use, can compare results with other data, and on the basis of such comparisons can change the series of operations it performs. Digital computers are used for reservations systems, scientific investigation, data processing and word-processing applications, desktop publishing, electronic games, and many other purposes.

Analog Computer

An analog computer operates on continuously varying data in a completely opposite way to the digital computer. For a start, all operations in an analog computer are performed in parallel. Secondly, data are represented as physical quantities not as digital computer. A single capacitor (equivalent to the Digital’s computer use of a transistor) is fixed in it which represents one continuous variable.It is designed to process data in which the variable quantities vary continuously; it translates the relationships between the variables and electrical quantities, such as current and voltage that is set up in its electrical circuits. Because of this feature, analog computers were especially useful in the simulation and evaluation of dynamic situations, such as the flight of a space or the changing weather patterns over a certain area. Although analog computers are commonly found in such forms as speedometers and watt-hour meters, they largely have been made obsolete for general-purpose mathematical computations and data storage by digital computers.In Analog Computers, using properties of electrical resistance, voltages and so on often performs computations. For example, a simple two variable adder can be created by two current sources in parallel. The first value is set by adjusting the first current source (to say x milliamperes), and the second value is set by adjusting the second current source (say y milliamps). Measuring the current across the two at their junction to signal ground will give the sum as a current resistance x+y milliamps. Other calculations are performed similarly, using operational amplifiers and other circuits for other tasks.Analog computers, however, have been replaced by digital computers for almost all calculations. It may be stretching a point to regard some physical simulations such as wind tunnels as analog computers, because the data so obtained must then also be scaled. There is a point of view in physics based on information processing which attempts to map the physical processes to computations. Thus, from these points of view, the wind tunnel data gathering is either an experiment or a computation.A simple form of analog computation still in regular use is the monogram (A two-dimensional diagram designed to allow the approximate graphical computation of a function). These are examples of analog computers that have been constructed or practically used:
 Astrolabe.             An astrolabe consists of a circle marked in degrees (similar to a protractor) with a rotating arm attached at its center. When the 0° mark on the circle is aligned with the horizon, and a star (or other celestial body) "sighted" at the end of the movable arm, the position (in degrees) of the star can be read ("taken") off the calibrated circle (hence, "astro" = star + "labe" = to take)

Operational Amplifier.           An operational amplifier or op-amp is an electronic circuit module (normally built as an integrated circuit) which has a non-inverting input (+), an inverting input (-) and one output. The output voltage is the difference between the + and - inputs multiplied by the open-loop gain.

Water integrator.          The Water Integrator was an early analog computer built in the Soviet Union in 1936. It functioned by careful manipulation of water through a room full of interconnected pipes and pumps. The level of water in various valves (with precision to fractions of a millimeter) represented stored numbers, and the rate of flow between them represented mathematical operations. Amazingly this machine was capable of solving non-homogeneous differential equations.
Target Data Computer.           The Target Data Computer was an early electromechanical computer employed in American submarines during WWII. The TDC was designed to provide fire control solutions for torpedo launches against enemy ships. It was most effective against surface vessels, but also helped with hostile subs too. The machine had a wide array of complicated dials and switches and required the operator to input navigation readings from his own boat and the corresponding data from an observed target, and the TDC would report the correct firing angles and velocity. The TDC also had a sophisticated scope that allowed the operator to get an accurate fix on the target's range, speed and heading.
Hybrid Computer

A computer that is a combination of analog and digital computer systems. A hybrid computer uses analog-to-digital conversion and digital-to-analog conversion, and may input or output either analog or digital data. One use for these computers is in robotics.