it system.pdf

(COMPUTER ORGANISATION) Introduction :A computer is an electronics device which accepts users data as input, process the data as per the users instruction and produces the output in the user required format. Basic Organization of Computer/ Functional Block Diagram/ Von- Numan Architecture:...

(COMPUTER ORGANISATION) Introduction :A computer is an electronics device which accepts users data as input, process the data as per the users instruction and produces the output in the user required format. Basic Organization of Computer/ Functional Block Diagram/ Von- Numan Architecture: It describes the architecture of a general digital computer and it consists of following units (a) Input Unit (b) CPU (Central Processing Unit) (c) Output Unit (d) Memory Unit ALU CU Input Unit Output Unit Memory Memory Unit (Functional Block Diagram) (a) Input Unit: It is used to accept data & instructions from user. It converts the data & instructions into computer understandable format. Supply the converted data to the CPU for processing. Examples of different types of Input devices: Key board, Mouse, Image Scanner, Camera (web Cam), Microphone, Joy Stick, Optical Pen, Bar code Reader, and Optical mark Reader etc. (b) CPU Unit (Central Processing Unit): It is the main part of the computer and also called as the brain of the computer. It controls the overall activities of the computer and performs different types of operations. It mainly consists of 3 units (i) ALU (ii) CU (iii) Memory  (i) ALU (Arithmetic Logic Unit): This unit performs all the arithmetic and logical operations/ calculations inside the computer like Addition, Subtraction, Multiplication, Division, Logical AND, OR etc. (ii) CU (Control Unit): It is used for controlling the overall operations of a computer. It generates different signals for different activities like Read, Write operations. (iii) Memory: These are set of registers which are used to store data and intermediate results during an arithmetic and logical operation. (c) Output Unit: The output unit is used to produce or display results of processed data in used requirement format. The output result may be a soft copy or hard copy. Soft copy outputs are only visible and have no physical existence. Hard copy outputs have physical existence. Examples of different output devices: Monitor, Printer, Plotter, Speaker, Projector etc. (d) Memory Unit: It is used to store data, instructions and results. The memory of computer is divided into 2 types. (i) Primary Memory: o This is the memory where program is stored for its execution by CPU. o Execution of program is not possible until the program and data are loaded in this memory. o During the execution the result is also stored in main memory and after that it goes to the secondary memory for permanent storage. o Main memory is volatile in nature i.e the contents of this memory are goes out when power goes off. (ii) Secondary Memory: o As main memory is volatile in nature and limited capacity so in order to store large amount data permanently secondary/ auxiliary memory is used. o It consists of magnetic or optical materials and used to store data permanently even power is off. o Both read and write operation is possible here and data & programs need to load in main memory for their execution. Input Devices, CPU & Output Devices: Input Devices: In order to get output from a computer we have to enter data to the computer through different input devices. An input device is any hardware components through which user can insert data, instructions, and programs into the computer. Some of the most commonly used input devices are mentioned below. (i) Keyboard: The most commonly used input device is a keyboard. By the help of keyboard user can input letters, numbers and special characters in to different applications or programs. A keyboard also has a special character that helps to operate the computer. (ii) Mouse: Themouse is the most widely used pointing device. By the help of mouse user can work in graphical user interface. A mouse is an input device that is used to control the movement of the pointer on the computer screen and helps to make selection from the screen. (iii) Optical Mark Reader (OMR): The Optical Mark Reader is a special type of input device which is used to read carefully pencil/ pen marks on a specially designed OMR sheet. This device mostly used now days for conducting objective type examinations, questionnaires and in forms (iv) Scanner: Image Scanner is an input device that optically scans images, printed text or any object into digital image. By placing the picture on the flat transparent surface of the scanner, any hardcopy can be converted into digital form. Now a day’s scanners are also providing an Optical Character Recognition (OCR) technique which scans a text and gives us a text file. (v) Magnetic Ink Character Recognition (MICR): The Magnetic Ink Character Recognition is a special type of input device that recognizes special characters printed in magnetic ink and input rapidly to a computer. This technique is mainly used by banking system (in ATM) and other business organizations for identification purpose. (vi) Other Input Devices: The input devices are Camera, Microphone, Digital pen, joystick, touch screen etc. Output Devices: (i) Printer: Printers are used to produce the output in hardcopy format. The resolution of Printer is measured in the form of DPI (Dots Per Inch) or PPI (Pixel Per Inch). Printers are off 2 types (a) Impact Printer (b) Non-impact Printer (a) Impact Printer: Here physical contact occurs between print head and paper while printing. Ex. Dot-matrix printer, Daisy-wheel printer, Chain Printer etc. (b) Non- Impact Printer: Here no physical contact occurs between print head and paper while printing. Ex. Ink-jet printer, Laser printer etc. (ii) Plotter: A Plotter is a special output device that draws image with ink pens and also produce the output in hardcopy format. So a Plotter is a graphical printer used for making graphs, charts, maps & 3D graphics etc. Plotters are off 2 types (a) Drum Plotter (b) Flat bed Plotter. (a) Drum Plotter: This plotter has a drum. A paper wraps around the drum that rotates to produce plots. Pens are moving across the paper while the drum is turning. (b) Flat bed Plotter: This plotter has a bed. This is also called table plotter. Here paper is placed on the bed which is fixed. This is generally used for large drawing. Classification of Memory: Memory is an essential component of a digital computer. It is needed to store programs, data and results. The memory of computer is divided into following 5 types. (1) Register Memory (2) Cache Memory (3) Primary/ Main Memory (4) Secondary/ Auxiliary Memory (5) Backup Memory (1) Register Memory: This memory is present inside the processor. It consists of a set of general & special purpose registers These are used to store the intermediate results during an arithmetic & logical operation. Register memory is smaller but faster in nature. (2) Cache Memory: Since the size of register memory is very small, then most of cases CPU access the data stored in main memory. But since the memory access time for accessing main memory is relatively more, so CPU execution time is more. In order to avoid the delay, a small faster memory known as cache memory is used and it is present in between CPU and main memory. Cache is used to store frequently used programs and data. (3) Primary/ Main Memory: This is the memory where program is stored for its execution by CPU. Execution of program is not possible until the program and data are loaded in this memory. After the execution the result is also stored in main memory and after that it goes to the secondary memory for permanent storage. Main memory is volatile in nature i.e the contents of this memory are goes out when power goes off. These are semi-conductor memory and divided in to 2 types-(i) RAM (ii) ROM (i) RAM :  o RAM stands for Random Access Memory because here any memory location can be accessed directly and the time take to access any memory location is same. o This is volatile in nature i.e its content will be lost when power goes off. o Both read and write operation is possible here. o There are 2 types of RAM (a) Static RAM (b) Dynamic RAM (ii) ROM: o ROM stands for Read only memory because in this memory only read operation is possible. o The user is not allowed to write anything here, it was written by the manufacturer. o It is non-volatile in nature i.e its content will not be lost when power goes off. o ROM is also divided in to several types (a) PROM : Programmable ROM- here user is allowed to reprogram but only once. (b) EPROM : Erasable Programmable ROM : here contents of ROM can be erased and reprogrammed multiple times. Here the contents can be deleted using Ultraviolet light but the entire content can be erased at a time. (c) EEPROM : Electrically Erasable Programmable ROM : here contents of ROM can be erased by electrical signals. Here the advantage is user can erase the selected contents as per the requirement. (4) Secondary/ Auxiliary Memory: As main memory is volatile in nature and limited capacity so in order to store large amount data permanently secondary/ auxiliary memory is used. It consists of magnetic or optical materials and used to store data permanently even power is off. Both read and write operation is possible here and data & programs need to loaded in main memory for their execution (5) Backup Memory: It is an additional memory, which is used to store data in parallel with storage of data in secondary memory. The main purpose of this memory is to recover data after it lost. It is normally used in large organizations & business fields to provide additional level of security. Magnetic tape and CD are normally used as back-up memory.