Computer System And Organization Class 11 Notes | Computer Science

Computer System And Organization Class 11 Notes including CPU, Software, Operating System, Hardware, Memory, Cache Memory, Language Translator, System Software topics. Specially designed for the students learning class 11 Computer Science according to syllabus suggested by CBSE to secure high marks with better understanding in less time and effort.

What is computer system?

• A computer is basically an electronic machine meant for computing. It can be programmed to take data as input, process it and generate information as output.
• Computer system comes in various forms and sizes such as Desktop, Laptop, Tablet, Mainframe, Super Computer, Smartphone etc.
• A computer system is ideally combination of Hardware and Software.

Basic Structure of Computer System
Block Diagram of Computer System

Image 2 Given below represents the basic structure of computer system. the directed lines represent the flow of data and signal between the components.

Components of Computer System

A computer System primarily comprises of (Figure above):         

1. Input Device
2. Output Device
3. CPU
4. Memory
5. Storage Devices

Input Device

• The devices used for input data into computer system are termed as Input device.
• Input devices converts the input data into digital signal that is understood by computer system
• Examples: Keyboard, mouse, scanner, touch screen, microphone etc.
• Input data is temporarily stored in primary memory (RAM)

Output devices

• The devices which are responsible for displaying or producing information are termed as output device.
• Output devices converts digital signals into human understandable form.
• Examples: Monitor, Printer, Speaker, Plotter, Projector etc.
• Output data is temporarily stored in primary memory that can be stored later permanently in secondary memory.

CPU

• CPU stands for Central Processing Unit referred as brain of computer
• It is responsible for all the processing done on data
• It performs arithmetic and logical operation on data as per the instructions given by the program it fetches from memory
• CPU has three main components
  • Registers: these are part of CPU and used to store data and instructions during operation being performed in limited size.
  • ALU: stands for arithmetic and logical unit that performs all the arithmetic and logical operations on data as per instructions of a program
  • CU: stands for Control unit which
    • Controls flow of data between memory, input and output devices.
    • Controls execution of instructions in sequential manner.

Computer Memory

Computer memory as it name implies, used to store data and instructions used for processing.

Types of memory

Computer systems have two types of memory

• Primary memory
• Secondary memory

Primary memory

• It stores data and programs temporarily during operation.
• CPU can read and write data directly to and from primary memory
• It is volatile in nature as its content gets deleted as soon as power supply is turned off.
• It is of two types
  • RAM:
    • Stands for Random Access Memory, used to store data temporarily during operation being performed.
    • It is volatile in nature
    • It is considered as main memory of computer system
    • The required program and data of any application while being started takes space in RAM.
    • It is faster than secondary memory
  • ROM
    • Stands for Read Only Memory, which stores startup programs that loads operating system into primary memory.
    • It is non-volatile in nature
    • Content of ROM cannot be modified.

Catch Memory

• It’s another type of Primary Memory which is considered as very high speed meory.
• It is placed between CPU and Primary Memory (RAM) referred as catche.
• The main purpose of Catch memory is to store the copies of frequently access data of primary memory to reduce the time consumed to access that data.

Secondary Memory

• It stores data and programs permanently that can be used in future also.
• It is non-volatile in nature.
• It has larger capacity but slower than primary memory.
• Content of secondary memory can not be accessed directly by CPU.
• Examples: SSD, HDD, CD/DVD, Flash Drive, Memory Card etc.

Unit of Memory

• Byte is unit of memory.
• 8 bits grouped together forms 1 Byte.
•  4 bits grouped together forms 1 nibble and 2 nibbles makes 1 Byte.

Given table shows different measurement units of data

Unit	Description
1 KB (KiloByte)	1024 Bytes
1MB (Mega Byte)	1024 KB
1GB (Giga Byte)	1024MB
1TB (Tera Byte)	1024GB
1PB (Peta Byte)	1024TB
1EB (Exa Byte)	1024PB
1ZB (Zetta Byte)	1024EB
1YB (Yotta Byte)	1024 ZB

Software

• Software refers to set of programs that instruct hardware what to do and how to do.
• It comprises of instructions and data to be processed using computer hardware.
• Each software is written for some computational purpose.
• Softwares are intangible.

Need of software

Software acts as an interface between user and hardware.

It makes computer hardware operational and useful.

Types of software

Software can be broadly classified in three categories:

• System software
• Application software
• Programming tools

System Software

It manages computer system by interacting directly with its constituent hardware.

It helps in providing various services to user and resources to other softwares.

Following are different types of System software:

• Operating System
• System Utilities (Utility Software)
• Device Drivers

Operating System

• The software that acts as an interface between user and computer hardware.
• It is a System Software.
• Every computer system must have at least one operating system installed.
• Windows, Linux, Solaris, MAC OS, Ubuntu, MS DOS are some of the examples of Operating System.
• It helps in performing the core functionalities like accepting input from various input devices, directing the output to the display, managing the files and directories, communicating with hardware, and installing /uninstalling of peripheral devices.

System Utilities

• System Utilities are Softwares used to maintain computer systems to work more smoothly, efficiently and effectively.
• It helps in improving the performance of computer
• It helps in providing security from virus
• It helps in managing and freeing disk space and providing data backups
• Disk defragmentation, formatting, system restore are some utilities inbuilt in Operating System.

Device Driver

• Device Drivers are programs that help functioning a hardware device with computer system
• It acts as an interface between the device and operating system.
• Overall control, interpretation, operation and management of a device at the hardware level is handled by device driver.

Programming Tools

Programming tools refers to the tools used to write instructions, converts high level to machine language and develop softwares for computer system.

Following are the programming tools used

• Programming languages
• Language translators
• Program development tools

Programming Languages:

• Programming languages are used to write instructions which are applied by computer system to get desire results.
• Programming languages are developed to simplify coding for computers.

Programming language can be classified in two categories:

• Low level language
• High level language

Low level language:

These are machine dependent language that includes:

• Machine language
• Assembly language

Machine language

• It uses binary code i.e. 0s and 1s to write instructions for computer system.
• It is directly understood by computer system and hence no intermediate software is required to execute them.
• It is difficult to use machine language as one has to remember all operational codes and machine addresses.
• It is difficult to find errors in the code written in machine language

Assembly language

• Assembly language uses English like words to write instructions for computer system.
• It is platform dependent means code written for a particular CPU cannot be used for another CPU.

High Level Language

• High level languages uses English like words using its own grammar (set of rules) to write instructions.
• It is platform independent and simple to write code.
• Translators (compilers) are needed to translate high level language into machine language.
• Examples: C++, Java, Python, C# etc.

Language Translators

• Language translators are used to convert instructions written in assembly or high level language to machine language.
• The code converted into machine language is called object code.

• Different translators for different languages are used for conversion.

There are three types of language translators:

• Assembler
• Compiler
• Interpreter

Assembler

• The translator used to convert the code written in assembly language to machine language is called assembler.
• Each assembler can understand a specific microprocessor instruction set only and hence, the machine code is not portable.

Compiler

• Compiler converts source code written in high level language into machine code.
• If the code does not follow all syntactic rules of the language, compiler generates error.
• Once source code is translated successfully, the compiler is not needed further.

Interpreter

• Interpreter converts source code written in high level language into machine code line by line.
• Interpreter is always needed whenever a source code is to be executed.

Program Development Tools

Program development tools are also referred as Integrated Development Environment which provides all resources needed for software development. It consist of:

• Text editor
• Debugger
• Compiler
• GUI Editor etc.

Examples: Python IDLE, Netbeans, Eclipse, Visual Studio, Atom

Application Software

• Software which is developed for a particular type of application such as drawing, presentation, documentation, calculation etc,
• It is used by user to accomplish their task.
• It always runs on the top of the system software.

There are two main categories of application software:

• General purpose software
• Customized software

General purpose software

• These are application software designed for generic applications such as Spreadsheets, Photoshop, and Chrome etc.
• These are developed to meet the requirement of mass users in mind without any geographical barrier.

Customized software

• These are application software designed to meet the requirement of individual or organization.
• Examples: school management software, hospital management, inventory management, payroll etc.

Operating system

• The software that acts as an interface between user and computer hardware.
• It is a System Software.
• Every computer system must have at least one operating system installed.
• Windows, Linux, Solaris, MAC OS, Ubuntu, MS DOS are some of the examples of Operating System.
• It helps in performing the core functionalities like accepting input from various input devices, directing the output to the display, managing the files and directories, communicating with hardware, and installing /uninstalling of peripheral devices.

Functions of Operating System

Functions of an Operating system can be broadly categorized as:

• Communication Management
• Resource Management
• Process Management
• File Management
• Memory Management

Communication Management

Establishes communication between different peripheral devices like printer, mouse, keyboard, monitor etc. Operating System uses special programs called drivers to identify these devices and their properties, to interact with them.

Resource Management

Here resource management refers to managing allocation and priority of different resources such as memory, CPU time, files, Input/output devices etc., to the various processes to get an optimum performance from the system. All these are discussed below:

Process Management

it refers to managing, controlling and scheduling different operations being executed in the CPU. It decides which process gets the processor and for how long.

Memory Management

it refers to dynamically allocating memory to the process to be executed and release when not needed.

File Management

It refers to managing all the files and folders in secondary memory. Creating, deleting, moving, copying or renaming are some common task performed on files.

OS User Interface

OS User Interface refers to medium through which user can interact with an Operating System.

Following are the commonly used interfaces of OS:

• Character (Command) user interface
• Graphical user interface
• Touch based interface
• Voice based interface
• Gesture based interface

Character (command) user interface

• In CUI commands are used as medium to exchange information between user and machine.
• The user has to remember name of all such commands which OS supports.
• The primary input device for CUI is keyboard.
• CUI based applications can perform only one task at a time.
• Examples of CUI based OS are: MS-DOS, UNIX

Graphical User Interface

• In GUI different graphics like icons, images, buttons, menus are used to interact with operating system.
• The primary input device for GUI is mouse.
• GUI based applications can perform more than one task at a time.
• Examples of GUI based OS are: Windows, Macintosh, Ubuntu, Federa etc.

Touch based Interface

• Now a days touch based interface applications are in use. Mostly build for smartphones and tablets.
• It allows user to interact with system simply using the touch input.
• Examples of touch based interface OS are : Android, Windows, iOS etc.

Voice based Interface

• Voice based interface OS allows user to interact with system by human voice.
• It is basically designed for the users who can use keyboard, mouse or touch screens.
• Voice based interface OS are: iOS(Siri), Android (Google), Window-10 (Cortana), OK Google etc.

Gesture based Interface

• Gesture based interface refers to interactive with system using different human gestures like waving, tilting, eye motion and shaking.
• Gesture based Interface is mostly supported by iOS and Android smartphones.
• Applications in gaming and medicine are majorly developing interface based on gestures.