Chapter 1 :

Computer Science Class XI ( As per CBSE Board)

Computer System & Organization

Introduction

• A computer is an electronic device, under the control of instructions stored in its memory that can accept data (input), process the data according to specified rules(Program), produce information (output), and store the information for future use
• Data vs Information
• Data are raw numbers or other findings which, by themselves, are
• of limited value.
• Information is data that has been converted into a meaningful and useful context.
• Computers are being used extensively nowadays in everyday life/every field In the form of laptop, desktop, smartphone,gadgets etc.

Functionalities of a computer

Any digital computer performs five functions in gross term.

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1. Take data as input
2. Stores data/instructions
3. Process those stored data
4. Generate the output
5. Control all above steps

Basic Computer Organization

Functional components of a computer

Input/Output Units Input Unit

A device through which data and programs from the outside world enter the computer system.

Output unit

A device through which results stored in the computer memory are made available outside the computer system.

Basic Computer Organization

• Control Unit
• Control unit
• It organizes the computer to work computer as single unit Arithmetic/Logic Unit
• Performs basic arithmetic operations such as addition and subtraction Performs logical operations such as AND, OR, and NOT.Most modern ALUs have a small amount of special storage units called registers that can be accessed faster than main memory.
• Memory
• A collection of cells, each with a unique physical address Most computers are byte-addressable
• Cell at address 11111110 contains 10101010

Basic Computer Organization

Memory Units

RAM and ROM

Random Access Memory (RAM)

It is read/write memory as it is possible to both read and write to a location within RAM. The RAM is volatile memory.

RAM chips in a computer can be categorized into two types:-

• SRAM
• DRAM

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Static RAM uses flip flops, which are circuits that can maintain their state without refreshing , to store data.

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Dynamic RAM uses transistors and capacitors to store data its need regular refresh cycles to prevent its contents from being lost.

SRAMs are faster than DRAMs and that is why are used in cache memory where as DRAMS are used in main memory.

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ROM:-

It is a read only memory , i.e the data and instructions are placed in the ROM at the time of its manufacturing and can't be changed there after. It is permanent and non-volatile memory as it does not lose its contents. ROM is slower than RAM.

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The different type of ROM available are:

• PROM (Programmable Read-Only Memory)
• EPROM (Erasable Programmable Read-Only Memory
• EEPROM (Electrically Erasable Programmable Read-Only Memory)

Secondary Storage Devices

Hard disk

Fixed Head HDD / Movable head HDD

A hard disk is a set of stacked disks. Each disk has data recorded electromagnetically in concentric circles, or tracks, on the disk Hard Drive Types

1. Parallel Advanced Technology Attachment (PATA)
2. Serial ATA (SATA)
3. Small Computer System Interface (SCSI)
4. Solid State Drives (SSD)

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Upto 12 TB sized HDD is available in the market

Input Devices

Input

devices can send data or information to a computer or another device. Keyboard: It is an input device which sends data in to the computer. The data send depends on the key pressed by the user.

Mouse: A mouse is a small handheld input device which controls a cursor in a graphical user interface. It can move and select text, files, folders etc. on our computer according to the user input.

Scanner: Scanner optically reads the document, file or image and then changes it into digital signal and sends to the computer.

OMR: optical mark recognition/ reader, is used to read marks or bubbles on documents, such as MCQ answer sheets ,survey or feedback form and send them to computer.

OCR: OCR stands for optical character Recognition, is an input device which converts scanned images of text into editable digital text.

MICR: Magnetic Ink Character Reader is an input device that can detect and interpret the magnetic ink characters on documents such as bank cheques. These devices are generally used in banking and financial institutions to process transactions.

Microphone: it receives audio generated by some input source and sends the same to a computer.

Webcam: it sends the captured images to a computer.

Graphics Tablets: This input device is used to draw using hand.

Barcode reader: It is used to read the barcode of various items and feed the same to computer.

Gamepad: Also known as joy pad is the input controller for video games. Joystick: these input devices are used to control video games.

Basic Computer Organization

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Output Devices

A device that can receive data from computer or another device and create output with that data is called output device. Examples of various output devices are as :

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Monitor: A monitor is an output device that is responsible for receiving data from a computer and displaying that information as text or images for users to see.

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Speakers: Receives sound signal from a computer and then plays that sound signal and thus we hear songs or music or any other audio.

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Projector: Gets data from a computer and displays or projects the same information onto a screen or a wall. Projector cannot directly accept data from a user and send that data to another device.

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Both Input / Output Devices

An input/output device is capable of receiving data from users or another devices and also sending data to another devices or computers. That means a devices which can be used as both input device and output device are called Input / Output (I/O) devices. Some examples of input/output devices are as:

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USB drive: Also known as pen drive or flash stick works as both input device to computer and as an output device. USB drives receive or save data from a computer as an input and it can also send data to a computer or another device.

Facsimile: Facsimile or FAX machine has a scanner which is an input device and a small printer to provide output.

Modems: It is used to transmit and receive data from one computer to another computer or other devices using telephone lines

CD-RW drives and DVD-RW drives: Receives data from a computer as input to copy onto and save into writable CD or DVD. We also use CDs or DVDs to transfer data to a computer.

Touch Screen: Touch screen is both input and output device. By touching the screen input is provided and being a screen, it is used as an output device.

Headsets: Headset consists of speaker as an output device and microphone

functions as an input device.

DEVELOPMENT OF COMPUTER

Abacus is known to be the first mechanical calculating device. Which was used to be performed addition and subtraction easily and speedily? This device was a first develop Ed by the Egyptians in the 10th centaury B.C, but it was given it final shape in the 12th centaury A.D. by the Chinese educationists.

NAPIER’S BONES John Napier’s of Scotland invented a calculating device, in the year 1617 called the Napier Bones. In the device, Napier’s used the bone rods of the counting purpose where some no. is printed on these rods. These rods that one can do addition, subtraction, multiplication and division easily.

Pascal's calculator In the year 1642, Blaise Pascal a French scientist invented an adding machine called Pascal’s calculator, which represents the position of digit with the help of gears in it.

Leibniz Calculator In the year 1671, a German mathematics, Gottfried Leibniz modified the Pascal calculator and he developed a machine which could perform various calculation based on multiplication and division as well.

Analytical Engine:-In the year 1833, a scientist form England knows to be Charles Babbage invented such a machine. Which could keep our data safely? This device was the first mechanical computer. Charles Babbage is also known as the father of the computer.

Basic Computer Organization

GENERATION OF COMPUTER

Software

It is an organized instructions/code written by programmers using any of various special computer languages for specific purpose.

Types of software:

1. Application software: It handles specialized/ common tasks a user wants to perform, such as banking, hotel management,any data processing, word processing etc.
2. System software: controls the basic functions of a computer and hides the complexity of computer system from user and application software. E.g. Operating System, Compiler, Interpret etc.
3. Utility software: Which helps to manage, maintain and control computer resources. E.g. are antivirus software, backup software and disk tools.

(1) System software

OPERATING SYSTEM

An Operating System (OS) is a system program that controls and manages the computer resources(resource manager) so that application software can run on it.

Example: Microsoft Windows, Solaris, Linux, MAC OS,Ubuntu, Apple’s i-Phone OS etc.

HOW OPERATING SYSTEM WORKS

In any computer or mobile device, the operating system can be termed as the back bone when it comes to software. This is because it has to be there before other programs can be run.It works as a middleman (interface) between machine and user.

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At the simplest level, an operating system does two things:

• It manages the hardware resources of the computer system. These resources include such things as the processor, memory, disk space, etc.

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• It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.

FUNCTIONS OF OPERATING SYSTEM

• Processor management

Loads, schedules and execute process/programs.

• Memory management

Allocates /De-allocation of memory for program execution.

• Device management

Communicate and controls various I/O devices.

• Storage management

Manages and controls the storage device to provide space to program for execution & data save.

• Application interface

API/drivers provide a way for applications to make use of hardware subsystems

• User interface

structure for interaction between a user and the computer

TYPE OF OPERATING SYSTEM

• Single-User, Single Task Operating System:

These operating systems work on single task & single user at a time.E.g. DOS

• Single-User, Multi-Task Operating System:

These operating systems works on more than one task and process them

concurrently at a time.E.g. windows 95 or later version of windows

• Multiuser Operating System:

In these OS, multiple users are allowed to access the same data or information at a time via a network. E.g. Unix,Linux,Windows7.

• Multiprocessing Operating System:

Here, a single process runs on two or more processors. All the processing and their management takes place in a parallel way, hence this OS are also called as Parallel Processing. E.g. Linux, UNIX and Windows 7.

• Embedded Operating System:

These are embedded in a device, which is located in ROM.E.g. OS of microwaves,washing machine.

• Distributed Operating System:

In these OS, the computers work in co-operation with each other.

SYSTEM SOFTWARE/PROGRAMMING SOFTWARES

Language processor/Programming Language

As the computer understand machine language(0/1) where as Humans

understand High level/Human Lang.

Language Processors does the coversion task(high level to machine lang.

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These are of 3 types Language processors

* Assembler * Compiler * Interpreter

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Compilers

It convert high-level language code to machine code in one session. It takes time because it have to translate high-level code to lower-level machine language all at once and then save the executable object code to memory.

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Interpreters

It translates code like a compiler but reads the code and immediately executes that code, and therefore it is initially faster than a compiler.

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Assemblers

It translates an assembly language program into machine language.

(2) Application software

* General Purpose application software

These are ready to use software for daily use purpose

e.g. word processor,spread sheet,presention,DBMS etc.

* Specific Purpose application software Softwares which are designed for specific task

e.g. Payroll,Hotel Mgmt,Hospital Mgmt,Stock Mgmt etc.

(3) Utility software

that assist OS in carrying out certain specialized tasks are called utility software.

• Antivirus - An anti-virus scans the system for any virus and if detected, gets rid of it by deleting or isolating it.
• Compression tools - Compression tools are utilities that assist operating systems in shortening files so that they take less space.

Software

(3) Utility software

• Disk Cleanup - Disk cleanup tools assist users in

freeing up disk space.

• Disk Defragmenter - Disk defragmenter is a disk management utility that increases file access speeds by rearranging fragmented files on contiguous locations.
• Backup - Backup utility enables backing up of files, folders, databases or complete disks.
• File management tools - Utility software providing regular file management tasks like browse, search, update, preview, etc. are called file management tools.

Memory units

What does a Computer Understands

Computers do not understand natural languages nor programming languages. They only understand the language of bits. A bit is the most basic unit in computer machine language. All instructions that the computer executes and the data that it processes is made up of a group of bits. Bits are represented in many forms either through electrical voltage, current pulses, or by the state of an electronic flip-flop circuit in form of 0 or 1.

1 Bit = Binary Digit(0 or 1)

8 Bits = 1 Byte

1024 Bytes = 1 KB (Kilo Byte) 1024 KB = 1 MB (Mega Byte) 1024 MB = 1 GB(Giga Byte)

1024 GB = 1 TB(Terra Byte)

1024 TB = 1 PB(Peta Byte)

1024 PB = 1 EB(Exa Byte)

1024 EB = 1 ZB(Zetta Byte) 1024 ZB = 1 YB (Yotta Byte) 1024 YB = 1 (Bronto Byte)

1024 Brontobyte = 1 (Geop Byte)

Boolean Logic

Because of computer understands machine language(0/1) which is binary value so every operation is done with the help of these binary value by the computer.

George Boole, Boolean logic is a form of algebra in which all values are reduced to either 1 or 1.

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To understand boolean logic properly we have to understand Boolean logic rule,Truth table and logic gates

Boolean Logic rules

Boolean Algebra is the mathematics we use to analyse digital gates and circuits. We can use these “Laws of Boolean” to both reduce and simplify a complex Boolean expression in an attempt to reduce the number of logic gates required.

Boolean Expression

A Boolean expression is a logical statement that is either TRUE or FALSE .

A Boolean expression can consist of Boolean data, such as the following:

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• BOOLEAN values (YES and NO, and their synonyms, ON and OFF, and TRUE and FALSE)

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• BOOLEAN variables or formulas

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• Functions that yield BOOLEAN results

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• BOOLEAN values calculated by comparison operators.

E.g.

1. $F(x, y, z) = x' y' z' + x y' z + x y z' + x y z
2. $F' (x, y, z) = x' y z + x' y' z + x' y z' + x y' z‘
3. $F(x, y, z) = (x + y + z) . (x+y+z') . (x+y'+z) . (x'+y+z)

Boolean Logic

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Truth table

A truth table is a mathematical table used in logic. e.g.

Boolean Logic

Logic Gates

Logic gate is

an idealized

or physical device implementing a Boolean

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function. These used construct logic cicuit

Boolean Logic

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Logic circuit

Construct a truth tables for following circuits of logic gates

Construct the logic circuit of following

1. C + BC:
2. AB+BC(B+C)

Boolean Logic

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Universal gates are the logic gates which are capable of implementing any Boolean function without requiring any other type of gate.

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Types of Universal Gates-

In digital electronics, there are only two universal gates which are-

1. NAND Gate
2. NOR Gate