Transcript CSL101: Introduction to Computers and Programming: Lecture 0

CSL101: Introduction to Computers and
Programming: Lecture 1: Introduction
Instructors
Prof Saroj Kaushik
Room No
:
Phone Number :
Email
:
Web Link
:
416, Bharati School building (CSE)
1292 (internal)
saroj@ cse.iitd.ernet.in
http://www.cse.iitd.ac.in/~saroj
Prof K K Biswas
Room No
Phone Number
Email
Web Link
313, Bharati School building (CSE)
6010 (internal)
[email protected]
http://www.cse.iitd.ac.in/~kkb
:
:
:
:
1st semester 2011-2012: Time Table
Lecture Time: 2.00-3.20 PM
Lect Venue : IV LT3
Practical: 11.00-12.50 PM (CSC): 2 hr/week lab for
each group
Cycle 1 : G1, 6 - Wednesday
Cycle 2 : G2, 7 - Thursday
Cycle 3 : G3, 8 - Friday
Cycle 4 : G4, 9 - Monday
Cycle 5 : G5, 10 -Tuesday
Course contents
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Introduction to Computers
Problem solving using computers
Development of algorithms?
Introduction to programming in a high level
language: Python
– Syntax and semantics
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Algorithms for various applications
Advanced features of Python
Number Representations
Sorting algorithms
Course Grading Structure
• These weights are indicative, and may
change as semester progresses
– Minor 1 & 2, each with 15-20% weightage
– Major, 30-35% weightage
– Quizzes and home assignments, 5-10%
weightage
– Programming exercises, 20-25% weightage
Submission of lab reports
• Labs will be conducted by TAs in CSC.
• Lecture slides, Lab exercises will be posted on web
or Moodle
http://www.cse.iitd.ac.in/~saroj
• For each exercise there will be a deadline for
submission of report/code.
• Be sure that you complete the exercise well before
the deadline and submit the report in time.
• We will not tolerate excuses (power fail, server
down, printer fault, lab closed, etc.).
• Heavy penalty for late submission
To pass the course
• A student has to pass EACH of the course components
indicated above, by getting at least 30% in each.
• Student should get minimum 35% overall to pass the course.
• Attend all classes and should be above 75%.
• Classes will begin on time and entry will not be allowed
later than 5 minutes.
• Cheating in tests or assignments will result in ‘F’ grade in
the course.
• Attend the “Special Help sessions” if you have difficulty in
the course.
• Keep meeting your TA ( Teaching Assistant) for any
difficulty in the course outside the lab timings as well.
Text books
• For Algorithm:
– R. G. Dromey “How to solve it by computer”,
Prentice Hall, Indian edition.
• Link to an online material on Python
Programming:
www.greenteapress.com/thinkpython/thinkpython.pdf
Introduction to Computers
What is a Computer?
• Electronic device
• Capable of performing
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arithmetic operations on numbers
logical operations on bits (binary digit)
decision test
retrieval, manipulation and storage of large
amount of data at a very high speed
What Does A Computer Do?
• Computers can perform four general
operations, which comprise the information
processing cycle.
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Input
Process
Output
Storage
• To do each of these computer has devices.
Devices that comprise a computer system
Monitor
(output)
Speaker
(output)
System unit
(processor, memory…)
Printer
(output)
Storage devices
(CD-RW, Floppy, Hard
disk, zip,…)
Scanner
(input)
Mouse
(input)
Keyboard
(input)
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Why Is a Computer So Powerful?
• The ability to perform the information
processing cycle with amazing speed.
• Reliability (low failure rate).
• Accuracy.
• Ability to store huge amounts of data and
information.
• Ability to communicate with other
computers.
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How Does a Computer Know what
to do?
• It must be given a detailed list of instructions,
called a computer program or software, that tells
what exactly it has to do.
• Before processing a specific job, the computer
program corresponding to that job must be created
and stored in memory.
• Once the program is stored in memory the
computer can start the operation by executing the
program instructions one after the other.
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Computer System
• A computer system is made up of both
– Hardware  electronic components
– Software  Program consisting of set of instruction
• Example: Some of the Anology:
– Mobile is hardware and corresponding
facilities available is software.
– CD is hardware and music on it is software.
Hardware Components Of A
Computer ?
• Input devices.
• Output devices.
• Central Processing
Unit
• Memory.
• Storage devices.
The Keyboard
• The most commonly used input device is the keyboard on
which data is entered by manually keying in or typing
certain keys.
• A keyboard typically has 101 or 105 keys.
The Mouse
• Is a pointing device which is used to control the movement
of a mouse pointer on the screen to make selections from
the screen.
• A mouse has one to five buttons. The bottom of the mouse
is flat and contains a mechanism that detects movement of
the mouse.
Output Devices
• Output devices make the information resulting from the
processing available for use.
• The two output devices more commonly used are the
printer and the computer screen.
• The printer produces a hard copy of your output, and the
computer screen produces a soft copy of your output.
The Central processing Unit, CPU
• The CPU contains electronic circuits that cause processing
to occur.
• Does the `work‘ of fetching, storing and manipulating
values that are stored in the computers memory.
• It is considered the “brain” of the computer.
Main Components of CPU
• Arithmetic Logic Unit (ALU)
– The ALU carries out arithmetic operations (e.g.
addition and subtraction) and logical operations
(e.g. and, or, not)
• Control Unit (CU)
– The CU controls the execution of instructions.
Memory
• Memory consists of electronic components
that store data including numbers,
characters, graphics and sound.
• It has two types of memory.
– Random Access Memory (RAM)
– Read only Memory (ROM)
Random Access Memory – RAM
• RAM is where programs and data are kept during
execution when the processor is actively using them.
• RAM is called Main memory or Primary memory.
• RAM
– Is Volatile - temporary
– Has random access to any memory location
– Read & write access
– Program + data reside in this memory
Main Memory
• Main memory is:
– very closely connected to the processor.
– the contents are quickly and easily changed.
– holds the programs and data that the processor
is actively working with.
– interacts with the processor millions of times
per second.
Read only Memory - ROM
• Read only Memory (ROM)
– Non volatile
– Only read access
– Permanent programs reside
Cache Memory
• A special and very high speed memory used to
increase the speed of processing.
• Cache is sometimes called CPU cache
• Transfer from cache to CPU is very fast as
compared to from main memory to CPU.
CPU
Main
Memory
ALU + CU
Cache
Cache Memory
• It lies between CPU and main memory.
• The cache is usually filled from main memory
when instructions or data are fetched into the CPU.
• Often the main memory will supply a wider data
word to the cache than the CPU requires, to fill the
cache more rapidly.
• It is expensive and usually small in size.
• Stores only segments of programs currently being
executed by CPU.
• It is also sometimes called buffer.
Storage Devices- Secondary memory
• Connected to main memory
• The contents are easily changed, but this is very slow
compared to main memory.
• It is used for long-term storage of programs and data.
• The processor only occasionally interacts with
secondary memory.
• The most common types of secondary storage used are
– Hard disks
– CD-ROM drives
– Flash Drives (USB, pen drives)
Hard Disk
• The hard disk has enormous storage
capacity compared to main memory
– 300 times the amount of storage in
main memory
• The hard disk is usually contained in
the systems unit of a computer.
Reasons for having two types of storage
Primary memory
Secondary memory
1.
2.
3.
4.
1.
2.
3.
4.
Fast
Expensive
Low capacity
Connects directly to
the processor
Slow
Cheap
Large capacity
Not connected
directly to the
processor
Data Representation in Memory
• Data is stored inside the memory in the
form of 1’s and 0s, Bits (Binary Digits) as
shown below (ON/OFF positions).
– For example
1100 0111
0011 1111
0101 1110
• One byte consists of 8 bits.
Contd…
• How many distinct values can be
stored in one byte?
• Answer:
28
• Minimum Value:
0
 0000 0000
• Maximum value:
28–1  1111 1111
Organization of Main Memory
• Main memory consists of a very long list of bytes.
• In most modern computers, each byte has an address that
is used to locate it.
• The picture shows a small part of main memory:
• Each row is called memory location that is a single
byte and has an address.
• The addresses are the integers to the left of the
boxes: 0, 1, 2, 3, 4, ... 255 for location of one byte.
• The addresses for most computer memory start at 0
and go up in sequence until each byte has an
address.
• The bits at a memory location are called the
contents of that location.
• Each location contains a pattern of eight bits, each
bit is either 0 or 1.
• When people say that a computer has "128 MB of
RAM" they are talking about how big its main
memory is.
Units of Memory
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1 KB (1 KiloByte) contains 1024 Bytes.
1 MB (1 MegaByte) consists of 1024 KB.
1 GB (1 GigaByte) has 1024 MB.
1 TB (1 Terabyte consists of 1024 GB.
Table of units of measurement
Name
Equivalent
Number of Bytes
power of 2
byte
8 bits
1
20
Kilobyte
(KB)
Megabyte
(MB)
Gigabyte
(GB)
Terabyte
1024 bytes
1024
210
1024 KB
1,048,576
220
1024 MB
1,073,741,824
230
1024 GB
1,099,511,627,776
240
Software
• Computer programmers/users write the codes/
instructions
that
make-up
software
applications/programs.
• Set of instructions is also referred to as lines of
code.
• Without software a computer is useless, just as a
car without someone to drive it.
• To get a computer to perform a specific task, it
must be given a sequence of unambiguous
instructions called a program written in some
programming language.
Types of Programs
• There are two categories of programs.
– Application
programs
(usually
called
just
"applications") that people use to get their work done.
– Systems programs keep all the hardware and software
running together smoothly.
• The difference between "application program" and
"system program" is fuzzy.
• Often it is more a matter of marketing than of
logic.
Application Programs
Systems Programs
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Word processors
Game programs
Spreadsheets
Data base packages
Graphics programs
Web browsers
Operating system.
Networking system.
Database system.
Compilers
Web site server.
Data backup.
Example of Types of Software
Application
Software
Operating
system Software
Operating Systems (OS)
• OS coordinates the operation of all the hardware and
software components of the computer system.
• The operating system is responsible for starting
application programs running and finding the
resources that they need.
• When an application program is running, the operating
system manages the details of the hardware for it.
• It is there in the background managing resources,
doing input and output for the application, and
keeping everything else running.
• The operating system is always present when the
computer is running.
Resources managed by OS
• OS is a complex collection of many programs that
governs the control of various resources such as:
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Processor
Main Memory
Secondary storage
I/O devices
Files
• The operating system is software; the same
hardware can be used with many different
operating systems (although only one at a time.)
Various Modules of OS
• There are various modules of OS
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Processor management
Memory management
Device management
Information management
• These modules resolve conflicts, optimize
performance and acts as an interface between the
user’s program and computer hardware.
• Modern operating systems usually come with a
user interface that enables users to easily interact
with application programs by using windows,
buttons, menus, icons, the mouse, and the
keyboard.
• Examples of operating systems are
– DOS, Unix, Windows 98, Windows NT, Linux,
Solaris, etc.
• There are different OS for different kinds of
machines.
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Single user machine
Batch processing
Multiprogramming
Time sharing
Real time machines
Programming Languages
Machine Lang
Assembly Lang
High level Lang
Consists of 0 & 1
Comp System
directly executes it
Pseudo inst
Add 2 5
Assembler translates
to M/L
English like insts
Input A, B
Compiler translates
to M/L
Difficult to write
Simple to write
Simpler to write
Highly error prone
Less error prone
Lesser error prone
Machine dependent
Machine dependent
Machine
independent
Machine Language
• Consider machine of 16-bits
Opcode (4-bits)
Address (12-bits)
• There are 16 possible opcodes (Hypothetical example)
Opcode
Action
0000
Load accumulator (ACC)from memory
0001
Store accumulator in memory
0010
Add the contents of Acc with specified
location and leave the result in ACC
1111
stop
M/L program
Instructions
Machine language
• Load ACC from Loc
10
• Add ACC with
contents of Loc 20
• Store ACC contents in
Loc 30
• Stop
• 0000 0000 0000 1010
• 0010 0000 0001 1010
• 0001 0000 0001 1110
• 1111 0000 0000 0000
Assembly Language
High level Language
(pascal, C, C++, Java)
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Load
Add
Store
Print
Stop
X
Y
Z
Z
Input X, Y
Z = X+Y
Output Z
Stop
One assembly instruction is equivalent to machine
instruction
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• One high level inst corresponds to many machine
instruction
• All CPUs have an instruction set (or language) that they
understand.
• Eventually all assembly level / high level programs must be
translated (or compiled) into instructions from this set.
• Roughly speaking, all processors have the same sort of
instructions available to them.
• An executable program is machine language program that runs
on a CPU and is always represented as a series of binary
digits.
• This is achieved by compiling (translating) a high-level
program with a special piece of software called a compiler.
• Compilers are incredibly complicated programs that accept
other programs as input and generate a binary executable
object file as output.
Types of Files
• As far as the hard disk is concerned, all files are the same and
are named collections of bytes. Of course, what the files are
used for is different.
• The OS can take a
– program file, copy it into main memory, and start it running.
– data file, and supply its information to a running program when it asks.
• Often then last part of a file's name (the extension) shows what
the file is expected to be used for. For example,
– "mydata.txt" the ".txt" means that the file is expected to be used as a
collection of text, that is, characters.
– “netscape.exe" the ".exe" means that the file is an "executable," that is, a
program that is ready to run.
– "program1.java" the ".java" means that the file is a source program in
the language java (there will be more about source programs later on in
these notes.)
– To the hard disk, each of these files is the same sort of thing: a
collection of bytes.
Example Problem :
Consider the problem of converting F (Fahrenheit) to C
(Centigrade) which is suitable for solution by computer.
Formula: C = 5 * (F – 32) / 9
• Set of possible high level instructions:
Input : F (given parameters)
Output: C (output parameters)
read F
C = 5 * (F – 32 ) / 9
print C
end
Compiler
• A source program is set of instructions written in a high level
language..
• It is translated into a machine language program by a system
software called compiler.
• It takes a source file as input and produces an executable
program (machine language program) as output.
• The source program is stored in a file created using a text
editor.
• The source file is kept on the hard disk.
• When you have to run your program (Source program), first
compile by compiler and form an executable file.
• The source file remains unchanged; a new executable file is
created.
• The executable file is also kept on hard disk.
• Compilers are specific to high level languages (like "C") and a
specific to processor type (like "Pentium"), and only runs
under a specific operating system (like "Windows".)
• The above is what goes on with most languages: Ada, Pascal,
C, C++, FORTRAN and others.
• Java adds a few more steps, which will be discussed later.
Interpreter
• There are some language which are not compiled but
interpreted by interpreter (BASIC, SML, Python …).
• An interpreter is a program that acts like a processor that
can directly execute a high level language.
• This is a fairly complicated thought. The figure might help:
• Here the source program "program.bas" has been written in
BASIC (a programming language) by a programmer with a
text editor.
• It is being interpreted by the BASIC interpreter, which is
running on the processor.
• The BASIC interpreter will read each command in the source
program and do what it says.
• When an interpreter is running a BASIC source program, both
the interpreter and the source program are in main memory.
• The interpreter consists of machine instructions that the
hardware can execute directly.
• Translator: takes a complete document in one language and
creates a complete document in another language, which can
then be used at any time.
• Interpreter: acts as an intermediate between source language
and machine language and converts instruction wise.