Computer Science Notes Unit 1 for Class XI A 2024 PDF

Computer Science Notes of Unit-I for Class XI A Unit 1: Introduction to Computer System 21.06.2024 to 05.08.2024 Index Topic Dates 1. Basic computer organization: Introduction to Computer System...

Computer Science Notes of Unit-I for Class XI A Unit 1: Introduction to Computer System 21.06.2024 to 05.08.2024 Index Topic Dates 1. Basic computer organization: Introduction to Computer System, hardware, software, input device, output device, CPU, memory (primary, cache and secondary), units of memory (bit, byte, KB, MB, GB, TB, PB) 2. Types of software: System software (Operating systems, system utilities, device drivers), programming tools and language translators (assembler, compiler, and interpreter), application software 3. Operating System(OS): functions of the operating system, OS user interface 4. Boolean logic: NOT, AND, OR, NAND, NOR, XOR, NOT, truth tables and De Morgan’s laws, Logic circuits 5. Number System: Binary, Octal, Decimal and Hexadecimal number system; conversion between number systems 6. Encoding Schemes: ASCII, ISCII, and Unicode (UTF8, UTF32) 1. Computer: A computer is an electronic device that can be programmed to accept data (input), process it and generate result (output). A computer along with additional hardware and software together is called a computer system. A computer system primarily comprises of a central processing unit, memory, input/output devices, and storage devices. All these components function together as a single unit to deliver the desired output. 2. Introduction to Computer System 2.1. Evolution of Computing Devices: Time Line: © Dr. Vimal K. Soni  2.2. Von Neumann Architecture It consists of a Central Processing Unit (CPU) for processing arithmetic and logical instructions, a memory to store data and programs, input and output devices and communication channels to send/receive the output data. Electronic Numerical Integrator and Computer (ENIAC) is the first binary programmable computer based on Von Neumann architecture. 2.3. Moore’s Law In 1965, Intel cofounder Gordon Moore introduced Moore’s Law which predicted that the number of transistors on a chip would double every two years while the costs would be halved. IBM introduced its first personal computer (PC) for the home user in 1981, Apple introduced Macintosh machines in 1984. The popularity of the PC surged by the introduction of Graphical User Interface (GUI) based operating systems by Microsoft and others in place of computers with only command line interface, like UNIX or DOS. Around 1990s, the growth of world wide web (WWW) further accelerated mass usage of computers and thereafter computers have become an indispensable part of everyday life. Further, with the introduction of laptops, personal computing was made portable to a great extent. This was followed by smartphones, tablets and other personal digital assistants. These devices have leveraged the technological advancements in processor miniaturisation, faster memory, high speed data and connectivity mechanisms. The next wave of computing devices includes wearable gadgets such as smart watch, lenses, headbands, headphones, etc. Further, smart appliances are becoming a part of the Internet of Things (IoT), by leveraging the power of artificial intelligence. 3. Components of a computer system and their interconnections: A computer system primarily comprises of a central processing unit, memory, input/output devices, and storage devices. Aforementioned figure shows the block diagram of a computer system. The directed lines represent the flow of data and signal between the components. © Dr. Vimal K. Soni 3.1. Central Processing Unit (CPU) It is the electronic circuitry of a computer that carries out the actual processing and is usually referred to as the brain of the computer. It is also commonly called 'processor' or ‘microprocessor’. The CPU is given instructions and data through programs. The CPU then fetches the program and data from the memory and performs arithmetic and logical operations as per the given instructions and stores the result back to memory. While processing, the CPU stores the data as well as instructions in its local memory, 'called' registers. Registers are part of the CPU chip and they are limited in size and number. Other than the registers, the CPU has two main components — Arithmetic Logic Unit (ALU) and Control Unit (CU). ALU performs all the arithmetic and logic operations that need to be done as per the instruction in a program. CU controls sequential instruction execution, interprets instructions and guides data flow through the computer’s memory, ALU and i/o devices. 3.2. Input Devices The devices through which control signals are sent to a computer are termed as input devices. These devices convert the input data into a digital form that computer system can understand. Example: keyboard, mouse, scanner, Camera, Joystick, touch screen, etc. Data entered through input device is temporarily stored in the main memory (RAM) of the computer system. For permanent storage and future use, the data as well as instructions are stored permanently in additional storage called secondary memory. 3.3. Output Devices The device that receives data from a computer system for display, physical production, etc., is called output device. It converts digital information into human understandable form. For example, monitor, projector, headphone, speaker, printer, etc. A printer is the most commonly used device to get output in physical (hardcopy) form. Three types of commonly used printers are inkjet, LaserJet and dot matrix. Now-a-days, there is a new type of printer called 3D-printer, which is used to build physical replica of a digital 3D design. These printers are being used in manufacturing industries to create prototypes of products. 3.4. System Interconnections and BUS: A bus is a communication system that transfers data between components inside a computer, or between computers. Computer systems generally consist of three main parts: The central processing unit (CPU) that processes data, The memory that holds the programs and data to be processed, and I/O (input/output) devices as peripherals that communicate with the outside world. Figure: Bus Interconnection Three types of System Bus Address bus - carries memory addresses from the processor to other components such as primary storage and input/output devices.... Data bus - carries the data between the processor and other components.... Control bus - carries control signals from the processor to other components. © Dr. Vimal K. Soni  4. Computer Memory A computer system needs memory to store the data and instructions for processing. Whenever we talk about the “memory” of a computer system, we usually talk about the main or primary memory. The secondary memory (also called storage device) is used to store data, instructions and results permanently and for future use. 4.1. Units of Memory A computer system uses binary numbers to store and process data. The binary digits 0 and 1, which are the basic units of memory, are called bit (acronym for Binary Digits). Further, these bits are grouped together to form words. A 4-bit word is called a Nibble. Examples of nibble are 1001, 1010, 0010, etc. A two-nibble word, i.e., 8-bit word is called a byte, for example, 01000110, 01111100, 10000001, etc. Like any other standard unit, bytes are grouped together to make bigger chunks or units of memory. Following Table shows different measurement units for digital data stored in computer memories. 4.2. Types of Memory Computers have two types of memories namely — Primary memory – for processing data (storing data for time-being to process) and Secondary memory – for storing data permanently © Dr. Vimal K. Soni  Primary Memory: Program and data are loaded into the primary memory before processing. The CPU interacts directly with the primary memory to perform read/ write operation. It is of two types viz. i) Random access memory (RAM), and ii) Read only memory (ROM). RAM is volatile i.e. as long as the power is supplied to the computer, it retains the data in it. But as soon as the power supply is turned off, all the contents of RAM are wiped out. It is used to store data temporarily while the computer is working. ROM is non-volatile, means its contents are not lost even when the power is turned off. It is used as a small but faster permanent storage for the contents which are rarely changed. For example, the startup program (boot loader) that loads the operating system into RAM is stored in a ROM. RAM is of two types: SRAM and DRAM BASIS FOR COMPARISON RAM ROM Basic It is a read-write memory. It is read only memory. store data to be currently required for booting of Use processed computer Volatility It is a volatile memory. It is a nonvolatile memory. Cost Costlier memory. Cheaper than RAM. Types of RAM are static RAM Types of ROM are MROM, Type and dynamic RAM. PROM, EPROM, EEPROM. MROM (masked read only memory) PROM (programmable read only memory) EPROM (erasable and programmable read only memory) EEPROM (electrically erasable and programmable read only memory) Differences between SRAM and DRAM: BASIS FOR SRAM(STATIC DRAM(DYNAMIC RAM) COMPARISON RAM) Speed Faster Slower Size Small Large Cost Expensive Cheap Used in Cache memory Main memory Construction transistors capacitors Present hence require power Charge leakage property Not present refresh circuitry Power consumption Low High Cache Memory: RAM is faster than secondary storage, but not as fast as a computer processor. So, because of RAM, a CPU may have to slow down. To speed up the operations of the CPU, a very high speed memory is placed between the CPU and the primary memory known as cache. It stores the copies of the data from frequently accessed primary memory locations, thus, reducing the average time required to access data from primary memory. When the CPU needs to access memory, it first examines the cache. In case the requirement is met, it is read from the cache, otherwise the primary memory is accessed. © Dr. Vimal K. Soni  Secondary Memory Primary memory has limited storage capacity and is either volatile (RAM) or read-only (ROM). Thus, a computer system needs auxiliary or secondary memory to permanently store the data or instructions for future use. The secondary memory is non-volatile and has larger storage capacity than primary memory. It is slower and cheaper than the main memory. But, it cannot be accessed directly by the CPU. Contents of secondary storage need to be first brought into the main memory for the CPU to access. Examples of secondary memory devices include SSD/ Hard Disk Drive (HDD), CD/ DVD, Memory Card, etc 5. Hardware and Software Computer Hardware refers to the computer's tangible components which includes the physical parts of a computer, such as the central processing unit (CPU), random access memory (RAM), motherboard, computer data storage, graphics card, sound card, and computer case. It also includes external devices such as a monitor, mouse, keyboard, and speakers. Hardware needs to be operated by a set of instructions. These sets of instructions are referred to as software. It is that component of a computer system, which we cannot touch or view physically. “The software comprises of set of instructions which on execution deliver the desired outcome.” A software knows how to make different hardware components of a computer work and communicate with each other as well as with the end user. We cannot talk to or instruct the hardware of a computer directly. Hence, software acts as an interface between human users and the hardware. Software can be broadly classified into three categories viz. i) System software ii) Programming tools and Language Translators iii) Application software. 6.1. System Software: The software that provides the basic functionality to operate a computer by interacting directly with its constituent hardware is termed as system software. A system software knows how to operate and use different hardware components of a computer. It provides services directly to the end user, or to some other software. System Software controls all internal activities inside a computer system and between all attached components of a computer system. Examples of system software include BIOS, operating systems, system utilities, device drivers etc. © Dr. Vimal K. Soni  BIOS: Basic Input Output System: BIOS is a computer program that is typically stored in EPROM and used by the CPU to perform start-up procedures when the computer is turned on. Operating systems: Operating system is a set of system programs that controls and coordinates the operations of a computer system. It provide interaction between user and computer. It also manages other application programs and provides access and security to the users of the system. Example: DOS, Windows. Unix, Linux, Android, Symbian, Major Functions of Operating System o Process Manager - Provide a structure for accessing an application o Memory Manager - Manage different types of memories o File Manager - Manage the files, folders and directory systems on a computer o Device Manager - Communicate with hardware and the attached devices. o Security Manager - A smart OS also provides a minimal security to the computer system through authorization (user name) and authentications (password) o Interface Manager - Provide a user interface – (CUI/TUI or GUI) ▪ CUI/TUI/CLI – Character User Interface/ Text User Interface/ Command Line Interface – ▪ GUI- Graphical User Interface- Easy to access and use o I/O Manager- manages all I/O operations o Network Manager - Provide basic networking structure for LAN and Internet o Manages Coordination among programs and users System utilities: Software used for maintenance and configuration of the computer system is called system utility. Some system utilities are shipped with the operating system, for example disk defragmentation tool, formatting utility, system restore utility, etc. Another set of utilities are those which are not shipped with the operating system but are required to improve the performance of the system, for example, anti-virus software, disk cleaner tool, disk compression software, etc. Device drivers: The device driver acts as an interface between the device and the operating system. It provides required services by hiding the details of operations performed at the hardware level of the device. Language Processors: It converts HLL Program to machine code/ executable code. Examples of Language processors: Assembler, Compiler and Interpreter An assembler is a computer program and a type of Language Processor that converts assembly language code into machine code that the computer can then read and execute. © Dr. Vimal K. Soni 6.2. Application Software: A software which used to carry out specific task is known as application software. Two categories of application software: General Purpose Software- The application software developed for generic applications, to cater to a bigger audience in general are called general purpose software. Such ready-made application software can be used by end users as per their requirements. For example: Adobe Photoshop, GIMP, Mozilla web browser, iTunes, etc Customized Software- These are custom or tailor-made application software, that are developed to meet the requirements of a specific organization or an individual. They are better suited to the needs of an individual or an organization, considering that they are designed as per special requirements. Some examples of user-defined software include websites, school management software, accounting software, etc. 6.3. Proprietary, Freeware & Free and Open Source Software Proprietary- When software to be used has to be purchased from the vendor who has the copyright of the software, then it is a proprietary software. Examples of proprietary software include Microsoft Windows, Tally, Quickheal Freeware- Software are freely available for use but source code may not be available. Such software is called freeware. Examples of freeware are Skype, Adobe Reader etc. Free and Open Source (FOSS)- Developers of some software allow public to freely use their software along with source code with an aim to improve further with each other’s help. Such software is known as Free and Open Source Software (FOSS). For example, the source code of operating system Ubuntu is freely accessible for anyone with the required knowledge to improve/add new functionality. More examples of FOSS include Python, Libreoffice, Openoffice, Mozilla Firefox, etc. © Dr. Vimal K. Soni