353584459-Chapter-1.pdfPhase Margin Determination Using LTSpice: A Comprehensive Guide

Python Programming
Using Problem Solving Approach
Reema Thareja
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© OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED.
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CHAPTER 1
Introduction to Computers and
Problem Solving Strategies

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What is a Computer?
A computer is an electronic machine that takes instructions and performs computations based on those
instructions.
Data is a collection of raw facts or figures.
Information comprises processed data to provide answers to ‘who’,‘what’,‘where’, and ‘when’ type of
questions.
Knowledge is the application of data and information to answer ‘how’ part of the question.
Instructions: Commands given to the computer that tells what it has to do are instructions.
Programs: A set of instructions in computer language is called a program.
Software: A set of programs is called software.
Hardware: A computer and all its physical parts are known as hardware.

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First Generation of Computers (1942 – 1955)
HardwareTechnology: Manufactured using thousands of vacuum tubes.
SoftwareTechnology: Programming was done in machine language or assembly language.
Used for: Scientific applications
Examples: ENIAC, EDVAC, EDSAC, UNIVAC I, IBM 701
Highlights: •They were the fastest calculating device of those times.
• Computers were too bulky and required a complete room for storage.
• Highly unreliable as vacuum tubes emitted a large amount of heat and burnt frequently.
• Required air-conditioned room for installation.
• Costly
• Difficult to use
• Required constant maintenance

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Second Generation of Computers (1955 – 1964)
HardwareTechnology: Manufactured using thousands of transistors.
SoftwareTechnology: Programming was done in high level language.
Used for: Scientific and commercial applications
Examples: Honeywell 400, IBM 7030, CDC 1604
Highlights: • Faster, smaller, cheaper, reliable, and easier to use than the first generation computers.
• Consumed 1/10th the power consumed by first generation computers.
• Bulky in size and required a complete room for its installation.
• Dissipated less heat than first generation computers but still required Ac room
• Costly
• Difficult to use
• Required constant maintenance

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Third Generation of Computers (1964 – 1975)
HardwareTechnology: Manufactured using thousands of integrated circuits.
Used for: Scientific, commercial and interactive applications
Examples: IBM 360/370, PDP-8, PADP-11, CDC6600
Highlights: • Faster, smaller, cheaper, reliable, and easier to use than the second generation computers.
•They consumed less power than second generation computers.
• Bulky in size and required a complete room for its installation.
• Dissipated less heat than second generation computers but still required AC room.
• Costly
• Easier to use and upgrade.

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Fourth Generation of Computers (1975 – 1989)
HardwareTechnology: Manufactured using Large Scale andVery Large Scale integrated circuits.
Used for: Scientific, commercial, interactive and network applications
Examples: IBM PC,Apple II,TRS-80,VAX 9000, CRAY-1, CRAY-2, CRAY-X/MP
Highlights: Faster, smaller, cheaper, powerful, reliable, and easier to use than the previous generation
computers

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Fifth Generation of Computers (1975 – 1989)
Hardware Technology: Manufactured using Ultra Large Scale integrated circuits. Use of Internet became
widespread. Very powerful mainframes, desktops, portable laptops, smartphones are being used commonly.
Super computers use parallel processing techniques.
Used for: Scientific, commercial, interactive, network and multimedia applications
Examples: IBM notebooks, Pentium PCs, SUM workstations, IBM SP/2, Param supercomputer
Highlights: • Faster, smaller, cheaper, powerful, reliable, and easier to use.
• Speed of microprocessors and the size of memory are growing rapidly.
• High-end features available on mainframe computers in the fourth generation are now available on the
microprocessors.
• Consume less power than computers of prior generations.
• Air-conditioned rooms required for mainframes and supercomputers but not for microprocessors.

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Characteristics of Computer
Speed:The speed of the computer is usually given in nano second and pico second, where
1 nano second = 1 × 10–9 second and 1 pico second = 1 × 10–12 second
Accuracy: Computer never makes mistakes. It always gives accurate results provided that correct data and
set of instructions are input to it.
Automatic: Computers are automatic devices that can perform without any user intervention
Diligence: Computer never gets tired. It can continually work for hours without creating any error.
Versatile:Versatile means flexible.Today, computers are being used in our daily lives in different fields.
Memory: Computers have internal memory (storage space) as well as external or secondary memory.
No IQ: Computers do not have any decision-making abilities of their own, i.e., their IQ level is zero.
Economical: Computers are considered as short-term investment for achieving long-term gain.

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Classification of Computer
Supercomputers: Supercomputer is the fastest, most powerful, and most expensive computer. A single
supercomputer can support thousands of users at the same time. They are mainly used for weather
forecasting, nuclear energy research, aircraft design, automotive design, online banking, controlling industrial
units, etc. Some examples of supercomputers are CRAY-1, CRAY-2, Control Data CYBER 205, and ETA A-10.
Mainframe Computers: Mainframe computers are large-scale computers. They are very expensive and need
a very large clean room with air conditioning. Mainframes can also support multiple processors. They are
typically used as servers on the World Wide Web. They are also used in organizations such as banks, airline
companies, and universities.
Minicomputers: Minicomputers are smaller, cheaper, and slower than mainframes. Minicomputers are used in
business, education, hospitals, government organizations, etc. While some minicomputers can be used only
by a single user, others are specifically designed to handle multiple users simultaneously. Minicomputers can
also be used as servers in a networked environment, and hundreds of PCs can be connected to it.

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Classification of Computer
Microcomputers: Microcomputers or PCs are very small and cheap.They can be classified into the following
categories:
• Desktop can be placed flat on a desk or table. It is widely used in homes and offices.
• Laptops are small microcomputers that can easily fit inside a briefcase.They are very handy and can easily
be carried from one place to another.
• Workstations are single-user computers.Their processing speed matches that of a minicomputer or
mainframe.They have advanced processors, more RAM and storage capacity than PCs.Therefore, they
are more expensive and powerful than a normal desktop computer.
• Network Computers have less processing power, memory, and storage than a desktop.They are designed
to be used as terminals in a networked environment. For example, to access data stored on a network.
• Handheld Computers include Smartphones,Tablet PCs and Phablets.

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Basic Applications of Computer
• Communication
• Desktop Publishing
• Government
• Traffic Control
• Legal System
• Retail Business
• Sports
• Music
• Movies
• Travel andTourism
• Business and Industry
• Hospitals
• Simulation
• Geology
• Astronomy
• Education
• Weather Forecasting
• Online Banking
• Industry and Engineering
• Robots
• Decision Support Systems
• Expert System
• Find jobs on the Internet
• Find a suitable match for a boy or girl
• Read news and articles online
• Find one’s batchmates
• Send and receive greetings

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Stored Program Concept
All digital computers are based on the principle of stored program concept, which was introduced by Sir
John von Neumann in the late 1940s.The following are the key characteristic features of this concept:
• Before any data is processed, instructions are read into memory.
• Instructions are stored in the computer’s memory for execution.
• Instructions are stored in binary form (using binary numbers—only 0s and 1s).
• Processing starts with the first instruction in the program, which is copied into a control unit circuit.
The control unit executes the instructions.
• Instructions written by the users are performed sequentially until there is a break in the current flow.
• Input/ Output and processing operations are performed simultaneously. While data is being
read/written, the central processing unit (CPU) executes another program in the memory that is ready
for execution.

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Components and Functions of Computer System
Input: process of entering data and instructions (also known as programs) into the computer system.
Storage: Process of saving data and instructions permanently in the computer so that it can be used for
processing.
Primary Storage also known as the main memory is that storage area which is directly accessible by the CPU at a
very fast speed. It is used to store the data and program, the intermediate results of processing and the recently
generated results.
Secondary Storage also known as secondary memory is cheaper, non-volatile and used to permanently store data
and programs of those jobs which are not being currently executed by the CPU.
Processing: The process of performing operations on the data as per the instructions specified by the user
(program) is called processing.
Output: Process of giving the result of data processing to the outside world (external to the computer system).
Controlling: The function of managing, coordinating, and controlling all the components of the computer system
is handled by the control unit, a part of CPU. © OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED.

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Components and Functions of Computer System

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Concept of Hardware and Software
Hardware: All the physical parts that can be touched are called hardware.
Software: The hardware needs a software (a set of programs) to instruct what has to be done.A program is a
set of instructions that is arranged in a sequence to guide a computer to find a solution for the given problem.
The process of writing a program is called programming.

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CPU Architecture
ALU: It performs all kinds of calculations, such as arithmetic, comparison and other operations.
Control Unit: It directs and coordinates the computer operations. It interprets the instructions (program)
and initiates action to execute them.
Register: It is a computer memory that provides quick access to the data currently being used for processing.
The ALU stores all temporary results and the final result in the processor registers
Accumulator and general-purpose registers:These are frequently used to store the data brought from the
main memory and the intermediate results during program execution.
MAR stores the address of the data or instruction to be fetched from the main memory.
MBR stores the data or instruction fetched from the main memory
IR stores the instructions currently being executed.
I/O register is used to transfer data or instructions to or from an I/O device.
Program counter stores the address of the next instruction to be executed. © OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED.

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CPU Architecture

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Input Devices
An input device is used to feed data and instructions into the computer.
Some of the input devices that are widely used by computer users to feed data or instruction to the computer
are keyboard, mouse, trackball, joystick, stylus, touch screen, barcode reader, optical character recognition
(OCR) device, optical mark recognition (OMR), MICR, web and digital cameras, etc.

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Output Devices
Any device that outputs/gives information from a computer is called an output device.
Soft copy output devices are those O/P devices which produce an electronic version of an output. Features of a soft
copy O/P are:
•The output can be viewed only when the computer is switched On.
•The user can easily edit the soft copy output.
• Soft copy cannot be used by people who do not have a computer.
• Searching data in a soft copy is easy and fast.
• Electronic distribution of a soft copy is cheaper. It can be done easily and quickly.
Hard copy output devices are those O/P devices which produce a physical form of output. Features of a hard copy •
Computer is not needed to see the output.
• Editing and searching the hard copy is difficult.
• Hard copy output can be easily distributed to people who do not have a computer.
• Distribution of a hard copy is not only costly but also slower. © OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED.

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Memory

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Memory Hierarchy
Cache memory is an intermediate form of storage between
registers and the primary memory. It is used to store
instructions and data that are repeatedly required to execute
programs thereby improving the overall system speed and
increase the performance of the computer. Keeping
frequently accessed data and instructions in the cache avoids
accessing the slower primary memory.

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Primary Memory - RAM
RAM is a volatile storage area within the computer typically used to store data temporarily so that it can be
accessed by the CPU. The information stored in RAM is loaded from the computer’s hard disk, and includes data
related to the operating system and applications that are currently being executed by the processor. There are two
types of RAM
Static RAM: This is a type of RAM holds data without an external refresh as long as it is powered. SRAM is made of
D flip-flops in which the memory cells flip-flop between 0 and 1 without the use of capacitors. Therefore, there is no
need for an external refresh process to be carried out. SRAM occupies more space and is more expensive than
DRAM
Dynamic RAM: This is the most common type of memory used in personal computers, workstations, and servers
today. A DRAM chip contains millions of tiny memory cells. Each cell is made up of a transistor and a capacitor, and
can contain 1 bit of information—0 or 1. To store a bit of information in a DRAM chip, a tiny amount of power is put
into the cell to charge the capacitor. Hence, while reading a bit, the transistor checks for a charge in the capacitor. If
a charge is present, then the reading is 1; if not, the reading is 0. © OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED.

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Primary Memory - ROM
ROM is non-volatile, that is, the data is retained in it even when the computer is turned off.
Rewritable ROM chips include PROMs, EPROMs, and EEPROMs.
• Programmable read-only memory (PROM) also called one-time programmable ROM can be written to or
programmed using a special device called a PROM programmer. The working of a PROM is similar to that
of a CD-ROM recorder which enables the users to write programs just once but the recorded data can be
read multiple times. Programming a PROM is also called burning.
• Erasable programmable read-only memory (EPROM) is a type of ROM that can be erased and re-
programmed. The EPROM can be erased by exposing the chip to strong ultraviolet light typically for 10
minutes or longer and then rewritten with a process that again needs higher than usual voltage applied.
• Electrically erasable programmable read-only memory (EEPROM) allows its entire or selected contents to be
electrically erased, then rewritten electrically.The process of writing an EEPROM is also known as flashing.

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Classification Of Computer Software
• Driver software
• Educational software
• Media players and media development software
• Productivity software
• Operating systems software
• Computer games
• Application software
• System software

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Operating System
An operating system is a group of computer programs that controls the computer’s resources such as CPU,
memory, I/O devices, etc. and provides the users with an interface that makes it easier to use.The primary
goal of an operating system is to make the computer system (or any other device in which it is installed, such
as a cell phone) convenient and efficient to use. It provides users an environment in which a user can execute
programs conveniently and efficiently. It is the most important software in a computer system.

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Translator
Compiler
A compiler is a special type of program that transforms the source code written in a programming language
(the source language) into machine language, which uses only two digits—0 and 1 (the target language). The
resultant code in 0s and 1s is known as the object code. The object code is used to create an executable
program.
If the source code contains errors, then the compiler will not be able to do its intended task. Errors that limit
the compiler in understanding a program are called syntax errors.
Each high-level language has a separate compiler. A compiler can translate a program in one particular high-
level language into machine language.

© OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED. 28
Translator
Interpreter
Interpreter translates the instructions into an intermediate form, which it then executes.The interpreter takes
one statement of high-level code, translates it into the machine level code, executes it, and then takes the next
statement and repeats the process until the entire program is translated.

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Translator
Assembler Since computers can execute only codes written in
machine language, a special program, called the assembler, is
required to convert the code written in assembly language into an
equivalent code in machine language, which contains only 0s and 1s.
There is a one-to-one correspondence between the assembly
language code and the machine language code. However, if there is
an error, the assembler gives a list of errors. The object file is
created only when the assembly language code is free from errors.
The object file can be executed as and when required. For example,
MASM,TASM, NASM,YASM,VASM, etc.

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Translator
Linker
Software development in the real world usually follows a modular approach in which, a
program is divided into various (smaller) modules as it is easy to code, edit, debug, test,
document, and maintain them. Moreover, a module written for one program can also be
used for another program. When a module is compiled, an object file of that module is
generated.
Once the modules are coded and tested, the object files of all the modules are combined
together to form the final executable file. Linker, also called a link editor or binder, is a
program that combines the object modules to form an executable program.
Loader
A loader is a special type of program that is part of an operating system and which
copies programs from a storage device to the main memory, where they can be
executed.

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Representation Of Data
Bit is a short form of binary digit. It is the smallest possible unit of data. In computerized data a bit can either be 0 or 1.
Nibble is a group of four binary digits.
Byte is a group of eight bits. A nibble is a half byte. Bits 0 through 3 are called the low order nibble, and bits 4 through 7
form the high order nibble
Word is group of two bytes is called a word. Bits 0 through 7 form the low order byte and bits 8 through 15 form the high
order byte.

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Problem Solving Strategies
In requirements analysis, user’s expectations are gathered to know why the software has to
be built.
In the design phase, a plan of actions is made before the actual development process can
start.
In implementation phase, the designed algorithms are converted into program code using
any of the high-level languages.
During testing, all the modules are tested together to ensure that the overall system works
well as a whole product.
In software deployment, training, and support phase, the software is installed or deployed in
the production environment.
Maintenance and enhancements are ongoing activities that are done to cope with newly
discovered problems or new requirements

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Algorithms
An algorithm provides a blueprint to writing a program to solve a particular problem. It is considered to be
an effective procedure for solving a problem in a finite number of steps.Algorithm should be:
• Be precise
• Be unambiguous
• Not even a single instruction must be repeated infinitely.
• After the algorithm gets terminated, the desired result must be obtained.
Different Approaches to Design an Algorithm
Top-down approach starts by dividing the complex algorithm into one or more modules.
Bottom-up approach is just the reverse of top-down approach. In the bottom-up design, we start with designing
the most basic or concrete modules and then proceed towards designing higher level modules.

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Control Structures Used in Algorithms
Sequence means that each step of the algorithm is executed in the specified order.
Decision statements are used when the outcome of the process depends on some condition
Repetition, which involves executing one or more steps for a number of times, can be implemented using
constructs such as the while, do-while, and for loops.
Recursion is a technique of solving a problem by breaking it down into smaller and smaller sub-problems
until you get to a small enough problem that it can be easily solved. Usually, recursion involves a function
calling itself until a specified condition is met.
Examples:

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Flowcharts
A flowchart is a graphical or symbolic representation of a process. It is basically used to design and
document virtually complex processes to help the viewers to visualize the logic of the process.
Example: Draw a flowchart to calculate the sum of the first 10
natural numbers.

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Flowcharts
Example: Draw a flowchart to add two numbers. Example: Draw a flowchart to determine the largest of three
numbers.

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Pseudocodes
Pseudocode is a compact and informal high-level description of an algorithm that uses the structural
conventions of a programming language. It facilitates designers to focus on the logic of the algorithm
without getting bogged down by the details of language syntax. An ideal pseudocode must be complete,
describing the entire logic of the algorithm, so that it can be translated straightaway into a programming
language.
Example: Write a pseudocode for calculating the price of a product after adding the sales tax to its original price.

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Types of Errors
Run-time errors occur when the program is being run executed. Such errors occur when the program
performs some illegal operations like dividing a number by zero, opening a file that already exists, lack of free
memory space, finding square or logarithm of negative numbers. Run-time errors may terminate program
execution.
Syntax Errors are generated when rules of a programming language are violated. Python interprets
(executes) each instruction in the program line by line. The moment interpreter encounters a syntactic error,
it stops further execution of the program.
Semantic or Logical Errors are those errors which may comply with rules of the programming language but
gives an unexpected and undesirable output which is obviously not correct. For example, if you write a
program to add two numbers but instead of writing ‘+’ symbol, you put the ‘-’ symbol.
Linker Errors These errors occur when the linker is not able to find the function definition for a given
prototype. © OXFORD UNIVERSITY PRESS 2017. ALL RIGHTS RESERVED.

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Testing
Unit Tests: Unit testing is applied only on a single unit or module to ensure whether it exhibits the expected
behavior.
Integration Tests: These tests are a logical extension of unit tests. In this test, two units that have already
been tested are combined into a component and the interface between them is tested.
SystemTests: System testing checks the entire system.

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Debugging
Debugging is an activity that includes execution testing and code correction. It locates errors in the program
code and fix them to produce an error-free code. Different approaches applied for debugging a code
includes:
Brute-Force Method: A printout of CPU registers and relevant memory locations is taken, studied, and
documented. It is the least efficient way of debugging a program and is generally done when all the other
methods fail.
Backtracking Method: It is used to debug small applications. It works by locating the first symptom of error
and then tracing backward across the entire source code until the real cause of error is detected. With
increase in number of source code lines, the possible backward paths become too large to manage.
Cause Elimination: A list of all possible causes of an error is developed. Then relevant tests are carried out to
eliminate each of them.

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