introduction to computers and...

Introduction to computers and programming

Content

• Hardware

• Information storage� RAM, ROM

� HD, DVD

• Display� Images

� Characters (fonts)

• File system/type� Encryption

� Compression

• Network� Protocols

� Packets

• Programming� Algorithm

� Pseudocode

� Flowchart

• Languages

• Source code� Example

The computer

Internally

The connections

Information storage

• 1 bit

• 8 bits

• 16 bits

• 32 bits

• 64 bits

• bit (1 or 0)

• byte (octet) (28)

• word (216)

• double (232)

• long double (264)

Encoding information on a fixed element of length n with a

base b gives bn non-redundant possibilities

Information coding

• Binary

� 0 or 1

• Octal

� 0-7

• Hexadecimal

� 0-9+A-F

• Decimal

� 0-9

• How to count

• 128+32+16+4+1=� 181 (decimal)

� 265 (octal)

� B5 (hexadecimal)

• Signed vs unsigned� 0 to 255

� -127 to +127

128 64 32 16 8 4 2 1

1 0 1 1 0 1 0 1

Operations on bits

• Booleans:

� 0 = false = no

� 1 = true = yes

• Operators:

� AND

� OR

� XOR

� NOT

• Example tablesAND 0 1

0 0 0

1 0 1

OR 0 1

0 0 1

1 1 1

XOR 0 1

0 0 1

1 1 0

RAM/ROM

Memory mapping

Address Values

0000

0001

0002

..

..

..

..

FFFF

• Size reminder:• Kilobyte Kb 210 ~103

• Megabyte Mb 220 ~106

• Gigabyte Gb 230 ~109

• Terabyte Tb 240 ~1012

• Petabyte Pb 250 ~1015

• …

1 0 1 1 1 0 0 1

0 0 0 0 1 1 1 1

1 1 1 0 0 0 1 1

0 0 1 0 0 1 0 0

HD/DVD

track

sector

head

Display

• Screen pixel or dots

• Color coding: 32 bits

• 1 pixel = 3 bytes of color (RGB)+1 byte alpha channel (transparency)

• 1600x1200x4bytes=7,5 Mb!

• Fonts

� Bitmap

� Vectors

� TrueType, OpenType, PostScript

QuickTime™ et undécompresseur TIFF (non compressé)sont requis pour visionner cette image.

Keyboard/Mouse

• Each key (or combination of keys) of the keyboard sends a code to the computer.

• The code is interpreted and converted to the corresponding ASCII or Unicode number.

• The mouse movements

� 1 to 4 bytes (vertical & horizontal)

• Buttons� Clicked, pressed, rolled

buttons

ASCII & Unicode

• ASCII 7/8 bits

• Unicode

� UTF-8/16/32 bits

� ISO-8859 (Latin)

• od -c od -h

•

Software layers

ROM

Hardware

Operating System

User Interface

Software

Files

CPU, RAM, HD, DVD

Word, scripts, mail, web browser…

Data (.doc, .mp3)

BIOS

Linux

CLI, X-Windows

Windows

Windows

MacOSX

Firmware

Quartz

File systems

• Method the OS uses to store information� Storage unit, directories, subdirectories (Windows,

VMS)

� Single arborescence (Linux, MacOSX, all Unix)

• What exactly is a file?� a piece of information (text, graphic, data, music

program, script)

� it is identified by a name and an logical address (or path)

� other informations: date, size, type, creator, ownership, physical address…

File system organisation

Disk 1 Disk 2

Directories

Subdirectories

Windows

DOCS PROGS

WORD EXCEL

CONFIG DATA

EXPT1 EXPT2

/

/usr /home

phil johnlocal

bin lib

emacs X11

Unix

D:C:

Disk 1

Disk 2

Path

• The path is the logical address used by the system or the user to locate a file.

• Example:/bd_du_Palais/35/etage/4/appart/12/Dupont_ Jean.txt

filenamesuffix

path

File types

• Executable� .exe

� .app

� Unix requires « x »

• Data� Text (.txt)

� Music (.mp3)

� Image (.jpg, .gif)

� Movie (.mpg, .mov)

� Binary (.bin)

• Special cases in Unix

� STDIN

� STDOUT

� STDERR

Encryption / compression

• Compression� Reducing the size of files

� E.g., .mp3, .gz, .jpg, .zip

• Encryption� Protecting your privacy

� E.g., .pgp

• Packing� Grouping the files

� E.g., .tar

Networks

• Direct� USB 11Mb-480Mb

� Ethernet 10Mb-1Gb

• Wired� Modem 56Kb

� ADSL 600Kb-8Mb

� LAN 10Mb-10Gb

• Wireless� Bluetooth 1Mb-20Mb

� WIFI (AirPort) 11Mb-54Mb

Network (ethernet or wireless)

• Computer talk to each other via network protocols

� ip, tcp, http, ftp, …

• TCP/IP� transmission control

protocol/internet protocol

• Handshaking

• Transmission

• Ackowledgement

• DNS� Domain Name Server

• URL� Universal Resource

Locator

• IP addess� 192.42.197.51

DNS reminder

Primary DNS

Root DNS

Local DNS

Client query Target server

1

2 3

45

6

www.expasy.org

129.194.8.64

*.org

dns.anywhere.net

client.anywhere.net

www.expasy.org ??

Packets

The data travels within units called packets

Packet breakout

Usual TCP/IP payload per packet: 512 bytes

Introduction to programming

What is a program?

• How to cook?

• The algorithm

• Are you a programmer?

Pseudocode

• This is the pseudocode for a game of Monopoly

Flowcharts

Flowcharts details

Languages

• Low level (processor dependent)

� Machine code, assembler

• High level: structured, procedural

� Fortran, C, Pascal…

• High level: object oriented

� C++, Java, C#, Perl, Objective-C…

• Virtual machines

� Java, C#…

• Scripting

� Perl, Python, JavaScript…

Source code -> Object code

• Compiler+linker� Fortran, C, Pascal, C++…

• Interpreter� Basic, Perl…

• Intermediate� Java

• Compiler+linker

� Fast to execute, but slow to debug

• Interpreter

� Slow to execute, but fast to debug (no need to recompile)

• Intermediate� Slow…

Source code

• Instructions

� Statement, blocks

� Affectation

� Operators

� Loops

� Tests

� Subroutines

� Comments

• Data structures

� Variable

� List

� Array

� Hash

� Pointers

� Objects

Source code (2)

• Statement, blocks� One or more

instructions for the processor

• Affectation� Change to a variable

• Operator� affect one or more

variable� + * - / AND OR NOT…

• Variable

� A region in memory that can be modified

� Exists in different types

� Scalar, char, numeric, boolean

� List, array

� Hash

� Combination->data structure

Source code (3)

• Loops� Allow the computer to

repeat blocks

• Tests� Decide what to do

• Subroutines� Programs frequently

called (functions)

• Comments� The most important

lines of the source code…

• Pointers

� Reference to region in memory (address)

• Objects

� Combination of data and code

Example: a text to treat

« Noon rings out. A wasp, making an ominous sound, a sound akin to a klaxon or atocsin, flits about. Augustus, who has had a bad night, sits up blinking and purblind. Ohwhat was that word (is his thought) that ran through my brain all night, that idiotic wordthat, hard as I'd try to pun it down, was always just an inch or two out of my grasp - fowlor foul or Vow or Voyal? - a word in a quizz which, by association, brought into play an

incongruous mass and magma of nouns, idioms, slogans and sayings, a confusing,amorphous outpouring which I sought in vain to control or turn off but which woundaround my mind a whirlwind of a cord, a whiplash of a cord, a cord that would split againand again, would knit again and again, of words without communication or any possibilityof combination, words without pronunciation, signification or transcription but out of

which, notwithstanding, was brought forth a flux, a continuous, compact and lucid flow: anintuition, a vacillating frisson of illumination as if caught in a flash of lightning or in a mistabruptly rising to unshroud an obvious sign - but a sign, alas, that would last an instantonly to vanish for good. »

Gilbert Adair

Result…

a=97

b=15

c=26

d=35

f=23

g=32

h=44

i=90

j=1

k=5

l=33

m=17

n=91

o=104

p=15

q=1

r=43

s=59

t=77

u=52

v=4

w=31

x=2

y=13

z=2

Do you see any problem??

Try with this:

« The quick brown fox, jumps over the lazy dog. »

Flowchart

Source code example

#!/usr/bin/perl -w # essential l ine of all perl scripts

$filename = "avoid.txt"; # affect « avoid.txt » to the variable $filename

# open the fi le, or exit

open(FILE, $filename) || die "Cannot open fi le ‘$filename’\n\n";

@text = <FILE>; # add each line of the file to an array

close FILE;

foreach $line (@text) { # read one line from the array into $line and repeat for each line

@table = split(//,$line); # read each character of the line in an array

while ($char=pop(@table)) { # read one character of the array 'table' and repeat for all

$char =~ s/[^a-z]//; # keep only the alphabetical character a to z

if ($char) { # check if the character exists and execute the block

$count{$char}++; # if yes, increment by one the hash 'count'

}

}

}

# print each character and its number of occurence one per l ine

foreach $c (keys %count) {

print "$c=$count{$c}\n";

}

exit; # quit the program

Tips

• Think about your problem

• Create a flowchart

• Create the pseudocode

• Verify the memory used by your variables

• Write the code

• Test the code

� For all the possible functions or cases (if possible)

� Give it to users as a beta (if not possibe)

� Sell it (if you work for Microsoft©… ;-)

• Debug

Summary of the week

• Monday

� Intro computers & programming

� Intro Unix

� Tutorial Unix

• Tuesday

� Intro Perl

� Regexp & Perl In-liners

• Wednesday� Object Oriented

programming

� BioPerl

� EMBOSS

• Thursday� Database indexing

� BLAST

� HTML & cgi-bin

• Friday� Finish exercises

� Users questions

Unix

• Next presentation…

Vassilios alias

UnixMan!!!