Chapter 1 Introduction To Computer System PDF

Chapter 1 INTRODUCTION TO COMPUTER SYSTEM Lecture3 A COMPUTER SYSTEM Any system is defined as a group of integrated parts which are designed to achieve a common objective. Thus, a system is made up of more than one element or part, where each element performs a specific f...

Chapter 1 INTRODUCTION TO COMPUTER SYSTEM Lecture3 A COMPUTER SYSTEM Any system is defined as a group of integrated parts which are designed to achieve a common objective. Thus, a system is made up of more than one element or part, where each element performs a specific function and where all the elements (parts) are logically related and are controlled in such a way that the goal (purpose) of the system is achieved. A computer is made up of a number of integrated elements like The central processing unit, The input and output devices and The storage devices. Each of these units performs a specific task. However, none of them can function independently on their own. They are logically related and controlled to achieve a specific goal. When they are thus integrated they form a fully fledged computer system. COMPONENTS OF A COMPUTER SYSTEM The basic parts of computer system are: Input Unit The Central Processing Unit Output Unit Central Processing Unit 1. The Input Unit 1. The Input Unit Input devices are the devices which are used to feed programs and data to the computer. The input system connects the external environment with the computer system. The input devices are the means of communication between the user and the computer system. Typical input devices include the keyboard, floppy disks, mouse, microphone, light pen, joy stick, magnetic tapes etc. The way in which the data is fed into the computer through each of these devices is different. However, a computer can accept data only in a specific form. Therefore these input devices transform the data fed to them, into a form which can be accepted by the computer. 1. The Input Unit These devices are a means of communication and inter station 1 between the user and the computer systems. Thus the functions of the input unit are : accept information (data) and programs. convert the data in a form which the computer can accept. provide this converted data to the computer for further processing. 1. The Input Unit Digitizer : A digitizer converts a graphical or pictorial data into digital form which can be directly entered and stored in a computer. A digitizer is also called as a graphics tablet. There are two types of digitizers : Image scan digitizer and flat bed digitizer In the image scan digitizer the entire image is scanned and reproduced automatically. Therefore the image scan digitizers are more powerful as compared to flat bed digitizers. Flat bed digitizers are mainly used in simple drawings, graphs etc. whereas image scan digitizers are used for photographs and pictures. 1. The Input Unit Scanner is able to directly enter text and images into the computer memory. Therefore, the duplication work of entering data is eliminated and this also results in increased accuracy. The speed of data entry also increases. There are two types of scanners : a. Optical Scanners b. Magnetic Ink Character Recognition devices 1. The Input Unit a. Optical Scanners The optical scanner uses a light source and sensor for reading the information on the paper. It can read characters, pictures, graphics from the paper. The common types of optical scanners are: 1. The Optical Mark Reader (OMR): This is capable of reading pre specified marks made by pencils or pens with the help of light. Light is focused on the page that is to be scanned. The reflected light pattern is detected by the device. These types of scanners are normally used where the data is preprinted for applications. eg. answer papers of the objective tests where the answers are marked with pencils or preprinted forms. 2. Optical Character Reader :The Optical Character Reader (OCR) can read alphabets, characters and numbers printed on paper. These characters can be either handwritten or typed. However special fonts are required to be used while typing. In case of handwritten data, the characters have to be of standard predefined size. The OCR reads each character as a collection of pixels. The light which is reflected from the page to be scanned is converted into binary data. OCRs are available in various sizes and speeds. These devices are expensive and are mainly used in processing where the data volumes are large.  Bar code reader is a device which reads bar coded data. Data which is coded in the form of light or dark lines (bars) is a bar code. Bar code readers are normally used in applications like labeling of products in retail shops, super markets etc. A laser beam scanner is used to read the bar code. The most commonly used bar code is the Universal Product Code (UPC). In this code the bars are coded as 10 digits. The first five digits define the manufacturer or supplier, and the remaining five digits denote the actual product of the manufacturer. b. Magnetic Ink Character Recognition (MICR): A special type of input device, this mainly finds application in banking areas. A magnetic ink is used to encode the characters to be read. This ink contains iron oxide particles. When a cheque is presented in the bank, the amount is encoded by the bank employee in the lower right corner and the cheque is then processed with MICR. Special character sets like E13B and CMC7 are used by these devices to encode data. The E13B has four special character and the digits 0-9. The CMC7 has five special characters, digits 0- 9, and all alphabets. The advantages of using MICR are that they speed up data entry, and even roughly handled cheque can be processed relatively easily. However, among the limitations are that special type of magnetic ink is required for.encoding characters and only a limited number of digits and characters are available for encoding. 2. The Central Processing Unit 2. The Central Processing Unit This is the brain of any computer system. The central processing unit or CPU is made of three parts: ØThe control unit. ØThe arithmetic logic unit ØThe primary storage unit a. The Control Unit The Control Unit controls the operations of the entire computer system. The control unit gets the instructions from the programs stored in primary storage unit interprets these instruction a subsequently directs the other units to execute the instructions. Thus, it manages and coordinates the entire computer system. b. The Arithmetic Logic Unit (ALU) The Arithmetic Logic Unit (ALU) actually executes the instructions and performs all the calculations and decisions. The data is held in the primary storage unit and transferred to the ALU whenever needed. Data can be moved from the primary storage to the arithmetic logic unit a number of times before the entire processing is complete. After the completion, the results are sent to the output storage section and the output devices. c. The Storage Unit Storage Unit: A storage unit is that part of the computer system which is used to store the data and instructions to be processed. There are two types of storage: 1) Primary storage Primary memory is also known as internal memory. This is a section of the CPU which holds program instructions, input data and intermediate results. Primary memory is also known as main memory. This is also called as Main Memory. Before the actual processing starts the data and the instructions fed to the computer through the input units are stored in this primary storage unit. Similarly, the data which is to be output from the computer system is also temporarily stored in the primary memory. It is also the area where intermediate results of calculations are stored. The main memory has the storage section that holds the computer programs during execution. Thus, the primary unit: Stores data and programs during actual processing Stores temporary results of intermediate processing Stores results of execution temporarily  The primary storage is volatile. Whenever the power is turned off the data is lost. Primary storage is also called Random Access Memory (RAM). RAM means it is possible to randomly select and use any storage location for storage and retrieval of data. RAM is also called a read/write memory because data can both be read from and written onto these units. When the power is switched off the data stored in the RAM is lost. ROM: ROM is Read Only Memory. In this type of memory the data is permanently stored. The information can only be read and new data cannot be written onto this memory. However the contentsof the ROM are not lost even when the power is turned off i.e. this memory is non-volatile. Such memories are also called as field stores, or permanent stores.  2) Secondary storage. Secondary storage is a memory that is stored external to the computer. It is used mainly for permanent and long term storage of programs and data. Examples: flash memory (rare) SSD (solid-state disk) units Hard disk drives (HDD) CD DVD 3. Output Unit 3. Output Unit The output devices give the results of the process and computations to the outside world. The output units accept the results produced by the computer, convert them into a human readable form and supply them to the users. The more common output devices are printers, plotters, display screens, magnetic tape drives etc. Answer the following What is the device(s) which considers as input & output device? Ø Oral Bonus Question new input & output technology