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 64 32 16 8
1
0
1
1
0
4
2
1
1
0
1
• 128+32+16+4+1=
 181 (decimal)
 265 (octal)
 B5 (hexadecimal)
• Signed vs unsigned
 0 to 255
 -127 to +127
Operations on bits
• Booleans:
 0 = false = no
 1 = true = yes
• Operators:




AND
OR
XOR
NOT
• Example tables
AND
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
1 0 1 1 1 0 0 1
0000
0 0 0 0 1 1 1 1
0001
1 1 1 0 0 0 1 1
0002
..
..
..
..
FFFF
0 0 1 0 0 1 0 0
• Size reminder:
•
•
•
•
•
•
Kilobyte
Megabyte
Gigabyte
Terabyte
Petabyte
…
Kb
Mb
Gb
Tb
Pb
210 ~103
220 ~106
230 ~109
240 ~1012
250 ~1015
HD/DVD
track
sector
head
QuickTime™ et un
décompresseur TIFF (non compressé)
sont requis pour visionner cette image.
•
•
•
•
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
Keyboard/Mouse
• Each key (or combination
• The mouse movements
of keys) of the keyboard
 1 to 4 bytes (vertical &
horizontal)
sends a code to the
computer.
• Buttons
 Clicked, pressed, rolled
• The code is interpreted and
converted to the
buttons
corresponding ASCII or
Unicode number.
ASCII & Unicode
• ASCII 7/8 bits
• Unicode
 UTF-8/16/32 bits
 ISO-8859 (Latin)
• od -c od -h
•
Software layers
Files
Data (.doc, .mp3)
Software
Word, scripts, mail, web browser…
User Interface
Quartz
CLI, X-Windows
Operating System
MacOSX
ROM
Firmware
Hardware
Windows
Windows
Linux
BIOS
CPU, RAM, HD, DVD
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
C:
DOCS
Disk 2
D:
PROGS
WORD
EXCEL
CONFIG
/
Directories
DATA
EXPT1
EXPT2
/usr
Disk 1
Subdirectories
local
phil
lib
bin
emacs
Windows
/home
Unix
X11
john
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
path
filename
suffix
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, …
• Handshaking
• Transmission
• Ackowledgement
• TCP/IP
• DNS
 transmission control
protocol/internet protocol
 Domain Name Server
• URL
 Universal Resource
Locator
• IP addess
 192.42.197.51
DNS reminder
3
Root DNS
2
*.org
4
5
Local DNS
Primary DNS
dns.anywhere.net
www.expasy.org
1
6
Client query
client.anywhere.net
www.expasy.org ??
Target server
129.194.8.64
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 a
tocsin, flits about. Augustus, who has had a bad night, sits up blinking and purblind. Oh
what was that word (is his thought) that ran through my brain all night, that idiotic word
that, hard as I'd try to pun it down, was always just an inch or two out of my grasp - fowl
or 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 wound
around my mind a whirlwind of a cord, a whiplash of a cord, a cord that would split again
and again, would knit again and again, of words without communication or any possibility
of combination, words without pronunciation, signification or transcription but out of
which, notwithstanding, was brought forth a flux, a continuous, compact and lucid flow: an
intuition, a vacillating frisson of illumination as if caught in a flash of lightning or in a mist
abruptly rising to unshroud an obvious sign - but a sign, alas, that would last an instant
only 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 line of all perl scripts
$filename = "avoid.txt"; # affect « avoid.txt » to the variable $filename
# open the file, or exit
open(FILE, $filename) || die "Cannot open file ‘$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 line
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!!!