Computer Notes PDF

of COMPUTER  What is Computer? Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use....

of COMPUTER  What is Computer? Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non- numerical (arithmetic and logical) calculations.  A computer has four functions:  a. accepts data Input  b. processes data Processing  c. produces output Output  d. stores results Storage  Input (Data): Input is the raw information entered into a computer from the input devices. It is the collection of letters, numbers, images etc.  Process: Process is the operation of data as per given instruction. It is totally internal process of the computer system.  Output: Output is the processed data given by computer after data processing. Output is also called as Result. We can save these results in the storage devices for the future use.  Computer System All of the components of a computer system can be summarized with the simple equations.  COMPUTER SYSTEM = HARDWARE + SOFTWARE+ USER  Hardware = Internal Devices + Peripheral Devices  All physical parts of the computer (or everything that we can touch) are known as Hardware.  Software = Programs Software gives "intelligence" to the computer.  First Generation (1940-56): The first generation computers used vaccum tubes & machine language was used for giving the instructions. These computer were large in size & their programming was difficult task.  The electricity consumption was very high. Some computers of this generation are ENIAC, EDVAC, EDSAC & UNIVAC-1.  In 2nd generation computers, vaccum tubes were replaced by transistors. They required only 1/10 of power required by tubes.  This generation computers generated less heat & were reliable. The first operating system developed in this generation.  The 3rd generation computers replaced transistors with Integrated circuit known as chip. From Small scale integrated circuits which had 10 transistors per chip, technology developed to MSI circuits with 100 transistors per chip.  These computers were smaller, faster & more reliable. High level languages invented in this generation.  LSI & VLSI were used in this generation. As a result microprocessors came into existence.  The computers using this technology known to be Micro Computers.  High capacity hard disk were invented.  There is great development in data communication.  Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today.  The use of parallel processing and superconductors is helping to make artificial intelligence a reality.  Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come.  Input Devices: Those devices which help to enter data into computer system. Eg. Keyboard, Mouse, Touchscreen, Barcode Reader, Scanner, MICR, OMR etc.  Output Devices: Those devices which help to display the processed information. Eg. Monitor, Printer, Plotter, Projector.  CENTRAL PROCESSING UNIT (CPU) The main component to make a computer operate is the computer chip or microprocessor.  This is referred to as the Central Processing Unit (CPU) and is housed in the computer case. Together, they are also called the CPU.  It performs arithmetic and logic operations. The CPU (Central Processing Unit) is the device that interprets and executes instructions.  Memory: It facilitates the remembrance power to computer system.  It refers to the physical devices used to store programs (sequences of instructions) or data (e.g. program state information) on a temporary or permanent basis for use in a computer or other digital electronic device.  The term primary memory is used for the information in physical systems which are fast (i.e. RAM), as a distinction from secondary memory, which are physical devices for program and data storage which are slow to access but offer higher memory capacity.  Primary memory stored on secondary memory is called virtual memory.  Primary Memory can be categorized as Volatile Memory & Non-Volatile Memory.  Volatile memory is computer memory that requires power to maintain the stored information.  Most modern semiconductor volatile memory is either Static RAM or dynamic RAM.  SRAM retains its contents as long as the power is connected and is easy to interface to but uses six transistors per bit.  Dynamic RAM is more complicated to interface to and control and needs regular refresh cycles to prevent its contents being lost.  However, DRAM uses only one transistor and a capacitor per bit, allowing it to reach much higher densities and, with more bits on a memory chip, be much cheaper per bit.  SRAM is not worthwhile for desktop system memory, where DRAM dominates, but is used for their cache memories..  Non Volatile Memory (ROM) Non-volatile memory is computer memory that can retain the stored information even when not powered.  Examples of non-volatile memory are flash memory and ROM/PROM/EPROM/EEPROM memory (used for firmware such as boot programs).  Cache Memory: Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM.  As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.  It is of two types- L1 cache is on the same chip as the microprocessor. L2 is usually a separate static RAM (SRAM) chip  Hard Disk (Local Disk)  Optical Disks: CD-R, CD-RW, DVD-R, DVD- RW  Pen Drive  Floppy Disks  Memory Cards  External Hard Disk  Blu Ray Disk  Blu-Ray Disk: Blu-ray (not Blue-ray) also known as Blu-ray Disc (BD), is the name of a new optical disc format.  The format offers more than five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc.  While current optical disc technologies such as DVD, DVD±R, DVD±RW, and DVD-RAM rely on a red laser to read and write data, the new format uses a blue-violet laser instead, hence the name Blu-ray.  The smallest unit is bit, which mean either 0 or 1. 1  bit = 0 or 1  1 Byte = 8 bit  1 Nibble = 4 bit  1 Kilo Byte = 1024 Byte = 210 Byte  1 Mega Byte = 1024 KB = 210 KB  1 Gega Byte = 1024 MB = 210 MB  1 Tera Byte = 1024 GB = 210 GB  1 Peta Byte =1024 TB = 210 TB  1 Exa Byte =1024 PB = 210 PB  1 Zetta Byte = 1024 EB = 210 EB  1 Yotta Byte = 1024 ZB = 210 ZB  NOTES of Computer Science  Operating system Operating system is a platform between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of a computer. It hosts the several applications that run on a computer and handles the operations of computer hardware. Functions of operating System: Processor Management Memory Management File Management Device Management  Types of Operating System Real-time Operating System: It is a multitasking operating system that aims at executing real-time applications. Example of Use: e.g. control of nuclear power plants, oil refining, chemical processing and traffic control systems, air  Single User Systems: Provides a platform for only one user at a time. They are popularly associated with Desk Top operating system which run on standalone systems where no user accounts are required. Example: DOS. Multi User Systems:Provides regulated access for a number of users by maintaining a database of known users. Refers to computer systems that support two or more simultaneous users. Another term for multi-user is time sharing. Ex: All mainframes are multi-user systems. Example: Unix  Multi-tasking and Single-tasking Operating Systems: When a single program is allowed to run at a time, the system is grouped under the single-tasking system category, while in case the operating system allows for execution of multiple tasks at a time, it is classified as a multitasking operating system. Distributed Operating System: An operating system that manages a group of independent computers and makes them appear to be a single computer is known as a distributed operating system. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they make a distributed system.  LANGUAGE PROCESSORS LANGUAGE PROCESSORS: Since a computer hardware is capable of understanding only machine level instructions, So it is necessary to convert the HLL into Machine Level Language. There are three Language processors: Compiler Interpreter Assembler  Compiler: It is translator which coverts the HLL language into machine language in one go. A Source program in High Level Language get converted into Object Program in Machine Level Language. Interpreter: It is a translator which converts the HLL language into machine language line by line. It takes one statement of HLL and converts it into machine code which is immediately executed. It eliminate the need of separate compilation/run. However, It is slow in processing as compare to compiler. Assembler: It translate the assembly language into machine code.  Internal Storage encoding of Characters ASCII( American standard code for information interchange): ASCII code is most widely used alphanumeric code used in computers. It is a 7- bit code, and so it has 27 =128 possible code groups. It represents all of the standard keyboard characters as well as control functions such as Return & Linefeed functions.  ISCII(Indian standard code for information interchange) : To use the Indian language on computers, ISCII codes are used. It is an 8-bit code capable of coding 256 characters. ISCII code retains all ASCII characters and offers coding for Indian scripts also.  Unicode: It is a universal coding standard which provides a unique number for every character, no matter what the platform, no matter what the program, no matter what the language. Unicode version 3.1 represented 94,140 characters.  Software Software, simply are the computer programs. The instructions given to the computer in the form of a program is called Software. Software is the set of programs, which are used for different purposes. All the programs used in computer to perform specific task is called Software.  Types of software 1. System software: Operating System Software DOS, Windows XP, Windows Vista, Unix/Linux, MAC/OS X etc. Utility Software Windows Explorer (File/Folder Management), Compression Tool, Anti-Virus Utilities, Disk Defragmentation, Disk Clean, BackUp, WinZip, WinRAR etc… Language Processors Compiler, Interpreter and Assembler 2. Application software: Package Software Ms. Office 2003, Ms. Office 2007, Macromedia (Dreamweaver, Flash, Freehand), Adobe (PageMaker, PhotoShop) Tailored or Custom Software School Management system, Inventory Management System, Payroll system, financial system etc.