Fran its definition, computer is said to be an electronic device, capable of accepting data as input, processes it and reveals it as result known as output. In our definition, we discover that computers mode of performance are input, process and output. Computer has its components as hardware and software in some cases human ware.
            Computer can be classified base on their principles of operation or on their configuration. By configuration, we mean the size, speed and storage capacity of computer. There are three (3) types at computers according to their principle of operation. These three (3) types of computer are: 

1.         Analog computer
2.         Digital computer
3.         Hybrid computer

            A digital computer is designed to process data in numerical form its circuits perform directly the mathematical operations of multiplication, addition, division and subtraction. The numbers operated on a digital computer are exposed in the Binary system. Binary digits can also be called BITS, which are O and 1, so that 0, 1, 10, 11, 100, 101, etc. corresponds to 0, 1, 2, 3, 4, 5, etc. binary digits are easily expressed in the computer circuits by the presence of (N) or absence (0) of a current or voltage. A series of eight consecutive bit is called “BYTE”, the eight bit byte permits 256 different “On – Off” combinations. Each bytes can thus represent one of up to 259 Alphanumeric characters and such an arrangement is called a “single Byte character set (SBCS); the factor standard of this extended ASC11 character set. The use of two bytes or 16 units for each symbol permits the representation of up to 65,536 character or ideograph. Such an arrangement is called “Double byte character set” (DBCS).         
            The operation of a digital computer are carried out by logic circuits which are digital circuits whose single output is determined by the condition of the input, usually two or more. Various circuits processing data in a computer operates in a highly synchronized manner and this is done by controlling then with an Oscillator which acts as computer clock. Operating at this speed, digital computer can perform thousand to trillion of arithmetic and logic operations per seconds.
            Before a computer can be used to solve a given problem, it must first be programmed i.e by given set of instructions or program. The various programs by which a computer controls aspects of its operation such as those for translating data from one form to another is known as “software” as contrast with “Hardware” which is the physical equipments. In some computer, the moment – moment control of the machine resides in a special software known as “operating system” (OS) or supervisor software is at great importance. Hence the usefulness of a highly sophisticated array of hardware can be served compromised by the lack of adequate software.
            A digital computer can store the results of its calculations for later use, and can computer result with other data and on the bases of such computer can change the series of operation if performs.
            Associated with the central processing units (CPU) or memory where results or other data are stored ranging from a small fraction of a second days or weeks before being retrieved for further processing. Once made up of vacuum tubes and later of small doughnut shaped ferromagnetic cores strung on a wire matrix, each of which consist of thousands of semiconductor devices. Where each vacuum or core represents one bit and the total memory of the computer was measured in thousand of bytes (or kilobytes i.e KB), each semiconductor device now represents millions of bytes (megabytes i.e. MB) and the total memory of mainframe computer is measured in billions of bytes (Gigabytes i.e. GB). Random Access Memory (RAM), which can be read from or written to, is lost each time the computer is turned off. Read Only Memory (ROM), which cannot be written to maintains its content at all times and its used to store the computers control information. Information and program storage, the major materials used today are magnetic tapes and  magnetic disc which can be read or written on and two types of optional disc, the compact disc (CD) and the digital dersatille disc (DVD0. DVD is an improved optical storage technology capable of storing vastly greater amount at data than the CD technology. CD-read-only memory and DVD-red-only memory discs are impressed with data at the factory but once being written, cannot be creased and rewritten with new data. But today both can be rewritten on. Most removable magnetic disc are commonly made at Mylar enclosed in a paper or plastic holder. Floppy disc have varying capacity, with very high density disc holding 250 MB to more than enough to contain a dozen at books. Non removable disc are made at metal and arranged in spaced layers. They can held more data and can read and write data much faster than floppies.
            Generally, transferring data is the slowest operation performed by a computer, especially when received or delivered to human beings. Time sharing used on large compallows different terminal to use a single computer at the same time. Each used only has the computer’s used for traction at the time, but the task switching is so rapid. Most computers in the world are stand-alone, single user device known as “personal computer” (PC) or workstations. It permits a user for example to have one file printed and another sorted while editing a third in a word processing session. Such computer can be linked in a network so that each computer is connected to others by the wires or coaxial cables, permitting all to share resources such as printers, modern and disc storage devices.    

            An analog computer is a device that works on continues range at values. The result given by the analog computer will only be approximated since they deal with quantities that varies continuously. It generally deals with variables such as voltage, pressures Temperature, speed e.t.c. The analog system is set up according to initial conditions and then allowed to change freely. Answers to the problems are obtained by measuring the variables in the analog model.       
            Most present-day electronic analog computer operate by manipulating potential differences (voltages). Their basic component is an operational amplifier, a device whose output current is proportional to its input potential difference. By causing this output current to flow though appropriate components, further potential differences are obtained and a wide variety at mathematical operations, including inversion, summation, differentiation, and integration can be carried out on them. Typical electronic analog computers consist of numerous types of amplifiers, which can be connected so as to build up a mathematical expression, sometimes at great complexity and with a multitude of variables.      
            Analog computer are especially well suited to stimulating dynamic systems such as simulations may be conducted in real time or at greatly accelerated rates, thereby allowing experimentations by repeated runs with altered variables. They have been widely used in simulations of aircraft, nuclear power plant, and industrial chemical processes. Other major uses includes analysis of hydraulic networks (e.g, flow at liquids through a sewer system) and electronics network (e.g, performance at long-distance circuits).
            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.

Hybrid Computer
            Hybrid computer are computers that inhibit features of analog computer 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. In general, analog computers are extraordinarily fast, since they can solve most complex equations of the rate at which a signal traverses the circuit, which is generally an appreciable fraction to the speed of at light. On the other hand, the precision of analog computers is not good; they are limited to three or at most, four digits of precision.
            Generally complex equation are approximated using Iterative Numerical methods which takes huge numbers of interactions, depending on how good the initial “guess” at the final value is and how much precisions desired. (this initial guess is known as the numerical seed for the interactive (process)
            Digital computer can be build to solve equation to almost unlimited precision but quite slowly compared to analog computers. Hybrid computers can be used to obtain a very good but relatively imprecise ‘seed’ value using an analog computer.
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