Any computer system consists of the four basic units; namely input unit, storage unit, central processing unit and output unit. Central Processing unit consists of Arithmetic logic unit and Control unit.
A computer performs five major functions no matter what size they are of as follows:
• Data or Instructions are accepted as input,
• Data and Instruction are stored
• Processing of data as per the instructions,
• Control of all operations inside the computer
• Result in the form of output.
Basic Components of Computer Systems
Following are the various components of a computer system–
Input Unit Data and instructions must enter the computer system before any computation can be performed on the supplied data. The input unit that links the external environment with the computer system performs this task. An input unit performs the following functions :
• It accepts (or reads) the list of instructions and data from the outside world.
• It converts these instructions and data in computer acceptable format.
• It supplies the converted instructions and data to the computer system for further processing.
The job of an output unit is just the reverse of that of an input unit. It supplied information and results of computation to the outside world. Thus it links the computer with the external environment. As computers to the outside world, it must be converted to human acceptable (readable) form. This task is accomplished by units called output interfaces.
Following functions are performed by an output unit.
• It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by us.
• It converts these coded results to human acceptable (readable) form.
• It supplied the converted results to the outside world.
The data and instructions that are entered into the computer system through input units have to be stored inside the computer before the actual processing starts. Similarly, the results produced by the computer after processing must also be kept somewhere inside the computer system before being passed on to the output units. The Storage Unit or the primary / main storage of a computer system is designed to do all these things. It provides space for storing data and instructions, space for intermediate results and also space for the final results.
The specific functions of the storage unit are to store:
• All the data to be processed and the instruction required for processing (received from input devices).
• Final results of processing before these results are released to an output device.
Central Processing Unit (CPU)
Central Processing Unit
The main unit inside the computer is the CPU. This unit is responsible for all events inside the computer. It controls all internal and external devices, performs “Arithmetic and Logical operations”. The operations a Microprocessor performs are called “instruction set” of this processor. The instruction set is “hard wired” in the CPU and determines the machine language for the CPU. The more complicated the instruction set is, the slower the CPU works. Processors differed from one another by the instruction set. If the same program can run on two different computer brands they are said to be compatible. Programs written for IBM compatible
computers will not run on Apple computers because these two architectures are not compatible.
The control Unit and the Arithmetic and Logic unit of a computer system are jointly known as the Central Processing Unit (CPU). The CPU is the brain of any computer system. In a human body, all major decisions are taken by the brain and the other parts of the body function as directed by the brain. Similarly, in a computer system, all major calculations and comparisons are made inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of a computer system.
Arithmetic and Logic Unit (ALU)
The arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of the instructions take place during the processing operations. All calculations are performed and all comparisons
(decisions) are made in the ALU. The data and instructions, stored in the primary storage prior to processing are transferred as and when needed to the ALU where processing takes place. No processing is done in the
primary storage unit. Intermediate results generated in the ALU are temporarily transferred back to the primary storage until needed at a later time. Data may thus move from primary storage to ALU and back again as
storage many times before the processing is over. After the completion of processing, the final results which are stored in the storage unit are released to an output device.
The arithmetic and logic unit (ALU) is the part where actual computations take place. It consists of circuits that perform arithmetic operations (e.g. addition, subtraction, multiplication, division over data received from
memory and capable to compare numbers (less than, equal to, or greater than).
The control unit directs and controls the activities of the internal and external devices. It interprets the instructions fetched into the computer, determines what data, if any, are needed, where it is stored, where to store the results of the operation, and sends the control signals to the devices involved in the execution of the instructions.
Register : In a computer, a register is one of a small set of data holding places that are part of a computer processor. A register may hold a computer instruction, a storage address, or any kind of data (such as a bit
sequence or individual characters).
Input devices include those devices with the help of which we enter data into computer as they make a link between user and computer. These devices translate the human readable information into the form understandable by computer. The various devices are as follows –
- Keyboard : Keyboard is among the most common and popular input device . It is used to input the data to the computer. In traditional times the typewriter was used. The keyboard has the layout similar to that of a typewriter but some additional keys are present that have additional functions.
- Mouse : Mouse is a cursor-control device . It is a pointing and drop device. It’s size is good enough to fit the palm. It has a palm size box with a round ball at its base .It senses the movement of mouse and
sends corresponding signals to CPU on pressing of the buttons. There are two buttons that provide the left click and the right click. A scroll bar is present in the mid .Mouse is only used to control the position
of cursor on screen.
- Joystick : Just like the mouse , Joystick is also a pointing device, which is used to move cursor position on a monitor screen. It has a stick that has a spherical ball at its both lower and upper ends. The lower
spherical ball moves in a socket. The joystick can be moved in four directions. It is mainly used in Computer Aided Designing (CAD) and playing computer games.
- Light Pen : Light pen is also a pointing device. Its structure is similar to that of a pen. It is based on an optical system placed in a small tube. It is used to select a displayed menu item or draw pictures on
the monitor screen. When light pen’s tip is moved over the monitor screen and pen button is pressed, its photocell sensing element, detects the screen location and sends the corresponding signal to the CPU.
- Track Ball : Track ball are used mostly in notebook or laptop computer. This is a ball, which is half inserted and by moving fingers on ball, pointer can be moved. A track ball requires less space than a
mouse as the whole device is not moved. A track ball can come in various shapes like a ball, a button and a square.
- Scanner : Scanner is an input device, which works on a similar principle of a photocopy machine. It is used when some information is available on a paper and it is to be transferred to the hard disc of the
computer for further manipulation.
Scanner captures images from the source which are then converted into the digital form that can be stored on the disc. These images can be edited before they are printed.
- Touch Screen : A touchscreen is an electronic visual display that the user can control through simple or multi-touch gestures by touching the screen with a special stylus/pen and-or one or more fingers. Some
touch screens use an ordinary or specially coated gloves to work while others use a special stylus/pen only. The user can use the touchscreen to react to what is displayed and to control how it is displayed (for example by zooming the text size).
- Digitizer : Digitizer is an input device which converts analog signal from the television camera into a strings of binary digits that can be stored in a computer. It converts the analog information into a digital
form. Digitizer is also known as Tablet or Graphics tablet. They can be used by the computer to create a picture of whatever the camera had been pointed at.
- Magnetic Ink Card Reader (MICR) : We see in banks, libraries etc using MICR as an input device . As large number of cheques are processed everyday MICR serves a very useful purpose. A special type of ink that contains particles of magnetic material that is machine readable, is used to read the code number and cheque number that are printed on the cheques in banks. This reading process is called Magnetic Ink Character Recognition (MICR). The main advantage of MICR is that it is highly accurate and fast in reading.
- Optical Character Reader (OCR) : OCR is an input device that is used to read a printed text. The role of OCR is to scan the text optically character by character by converting them into a machine readable
code and store the text on the system. The OCR is used for the preparation of electricity bills, insurance premium, telephone bills.
- OMR (Optical Mark Recognition): Optical mark recognition (also called optical mark reading and OMR) is the process of capturing human-marked data from document forms such as surveys and test.
- SCR (Smart Card Readers): A small electronic device about the size of a credit card that contains electronic memory, and possibly an embedded integrated circuit (IC). Smart cards containing an IC are
sometimes called Integrated Circuit Cards (ICCs).
Smart cards are used for a variety of purposes, including:
– Storing a patient’s medical records
– Storing digital cash
– Generating network IDs (similar to a token)
To use a smart card, either to pull information from it or add data to it, you need a smart card reader, a small device into which you insert the smart card.
- Bar Code Readers : Bar Code Reader is a device used for reading bar coded data (data in form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books, etc .Bar Code
Reader scans a bar code image by converting it into an alphanumeric values . This value is then fed to the computer to which bar code reader is connected.
- Microphone : A microphone,is an acoustic-to-electric transducer or sensor that converts sound in air into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systemsfor concert halls and public events, motion picture production, live and recorded audio engineering, two-way radios, megaphones, radio and television broadcasting, and in computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock sensors.
- Webcam : A webcam is a video camera that feeds or streams its image in real time to or through a computer to computer network. When “captured” by the computer, the video stream may be saved, viewed or sent on to other networks via systems such as the internet, and email as an attachment. When sent to a remote location, the video stream may be saved, viewed or on sent there. Unlike an IP camera (which connects using Ethernet or Wi-Fi), a webcam is generally connected by a USB cable, or similar cable, or built into computer hardware, such as laptops.
An output device is that component of computer hardware that communicates the results of data that is processed by the computer and converts the digital information into a form easily read and understood by humans.
Various Output devices are used in Computers.
- Monitors : Monitor or the Visual Display Unit (VDU) is the main output device of a computer. It forms images in the form of tiny dots, known as pixels. The sharpness of the image can be determined by the number of the pixels.
Two kinds of viewing screens are used for monitors:
• Cathode-Ray Tube (CRT)
• Flat-Panel Display
(a) Cathode-Ray Tube (CRT) Monitor : In the CRT, display consists of small picture elements known as pixels and determine the resolution of the image. Smaller are the pixels the better is the image clarity or resolution. Finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes that serve as a fixed location on the screen where a standard character can be placed. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically. However the CRT has some disadvantages as it is large in Size and has a high power consumption.
(b) Flat-Panel Display Monitor : These flat panel displays overcome the disadvantages of CRT as they have reduced volume, weight and power requirement compared to the CRT. They come in different
shapes and size. You can hang them on walls or wear them on your wrists. They are used in all modern day calculators, video games, monitors, laptop computer, graphics display etc as displays.
The flat-panel display are of two main types :
(i) Emissive Displays : The emissive displays convert electrical energy into light. Example are plasma panel and LED (Light-Emitting Diodes).
(ii) Non-Emissive Displays : The Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. Example is LCD (Liquid-Crystal Device).
(c) 3-D Monitors : It is a television that conveys depth perception to the viewer. 3-D describes an image that provides the perception of length. When 3-D images are made interactive then user feel involved
with the scene and this experience is called virtual reality.
- Printers : Printer is among the most common output device, which is used to print information on paper.
There are two types of printers:
• Impact Printers
• Non-Impact Printers
(a) Impact Printers : The printers that print the characters by striking against a ribbon and then onto the paper, are called impact printers.
Impact Printers are low of cost but they happen to be very noisy. Due to their low cost they are useful for bulk printing. There is physical contact with the paper to produce an image.
Impact printers can be further divided into two types:
(i) Character printers : These printers print one character at a time. These further divided into two such as the Dot Matrix Printer and the daisy wheel printer.
Dot matrix printer : They are the most popular printers because of their ease of printing features. They come at a low cost. Each character is printed in the form of pattern of Dot’s and head .These dots and heads consist
of a matrix of pins of size (57, 79, 97 or 99) that result in forming a character. Hence they are called as Dot Matrix Printer.
Daisy Wheel : These are known as daisy wheel printers as the head lies on the wheel and Pins correspond to characters like petals of Daisy flower. These printers are used for word-processing in offices and offer very nice quality representation.
(ii) Line Printers : Line printers are printers, which print one line at a time. Speed of line printers is limited by the speed of cartridge used.
These can be divided into two types: The drum printer and the Chain printer
Drum Printer : This printer looks like a drum in shape that’s why it is called a drum printer. The Drum surface has a number of tracks. Total tracks are equal to size of paper, i.e., for a paper width of 132 characters, Drum will have 132 tracks. A character set is embossed on track. The
different character sets available in market are 48 character set, 64 and 96 characters set. One rotation of drum leads to printing of one line. These printers print between 300 to 2000 lines per minute. Hence they have a very high speed.
Chain Printer : In this printer because chain of character sets are used hence they are called as Chain Printers. A standard character set may have 48, 64, 96 characters.
(b) Non-impact Printers : These printers print the characters without the physical contact with the paper i.e without striking against the ribbon and onto the paper. These printers print one complete page at a time, and are also called as Page Printers.
These printers are of two types: Laser Printers and the Ink-jet Printers.
(i) Laser Printers : These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page.
(ii) Inkjet Printers : Ink-jet printers are new technology non-impact character printers. They print characters via spraying small drops of ink onto paper. Ink-jet printers produce very high quality output with presentable features. They are noiseless printers and have many styles of printing modes available. These are also called as the coloured printers. Models of Ink-jet printers can produce multiple copies of printing also.
- Headphones : Headphones are referred to as earphones, headphones are a hardware device that either plugs into your computer (line out) or your speakers and allow you to privately listen to audio without
disturbing anyone else. The picture is an example of a USB headset from Logitech with a microphone and a popular solution for computer gaming.
- Speaker : A hardware device connected to a computer’s sound card that outputs sounds generated by the computer. It needs a sound card connected to a CPU, that generates sound via a card. These are used for listening music, for being audible in seminars etc.
- Projector : A projector is an output device that can take images generated by a computer and reproduce them on a large, flat (usually lightly colored) surface. For example, projectors are used in meetings to help ensure that all participants can view the information being presented.