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Introduction to computers and programming

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1 Introduction to computers and programming

2 Content Hardware Information storage Display File system/type Network
RAM, ROM HD, DVD Display Images Characters (fonts) File system/type Encryption Compression Network Protocols Packets Programming Algorithm Pseudocode Flowchart Languages Source code Example

3 The computer

4 Internally

5 The connections

6 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

7 Information coding Binary Octal Hexadecimal Decimal 0 or 1 0-7 0-9+A-F
How to count = 181 (decimal) 265 (octal) B5 (hexadecimal) Signed vs unsigned 0 to 255 -127 to +127

8 Operations on bits Booleans: Operators: Example tables 0 = false = no
1 = true = yes Operators: AND OR XOR NOT Example tables AND 1 OR 1 XOR 1

9 RAM/ROM Size reminder: Kilobyte Kb 210 ~103 Megabyte Mb 220 ~106
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

10 HD/DVD track sector head

11 Display Fonts Bitmap Vectors TrueType, OpenType, PostScript
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

12 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

13 ASCII & Unicode ASCII 7/8 bits Unicode od -c od -h UTF-8/16/32 bits
ISO-8859 (Latin) od -c od -h

14 Word, scripts, mail, web browser…
Software layers Files Data (.doc, .mp3) Software Word, scripts, mail, web browser… User Interface Quartz CLI, X-Windows Windows Operating System MacOSX Linux Windows ROM Firmware BIOS Hardware CPU, RAM, HD, DVD

15 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…

16 File system organisation
Disk 1 Disk 2 Disk 2 C: D: / DOCS PROGS CONFIG DATA Directories /usr /home Disk 1 WORD EXCEL Subdirectories EXPT1 EXPT2 local phil john bin lib emacs X11 Windows Unix

17 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 suffix filename path

18 File types Executable Data Special cases in Unix .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

19 Encryption / 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

20 Networks Direct Wired Wireless USB 11Mb-480Mb Ethernet 10Mb-1Gb
Modem 56Kb ADSL 600Kb-8Mb LAN 10Mb-10Gb Wireless Bluetooth 1Mb-20Mb WIFI (AirPort) 11Mb-54Mb

21 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

22 DNS reminder Primary DNS Root DNS Local DNS Client query Target server
1 2 3 4 5 6 *.org ??

23 Packets The data travels within units called packets

24 Packet breakout Usual TCP/IP payload per packet: 512 bytes

25 Introduction to programming

26 What is a program? How to cook? The algorithm Are you a programmer?

27 Pseudocode This is the pseudocode for a game of Monopoly

28 Flowcharts

29 Flowcharts details

30 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…

31 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…

32 Source code Instructions Data structures Statement, blocks Affectation
Operators Loops Tests Subroutines Comments Data structures Variable List Array Hash Pointers Objects

33 Source code (2) Statement, blocks Affectation Operator Variable
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

34 Source code (3) Loops Tests Subroutines Comments Pointers Objects
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

35 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

36 Result… Do you see any problem?? Try with this:
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. »

37 Flowchart

38 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 { # 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 { # 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

39 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

40 Summary of the week Monday Tuesday Wednesday Thursday Friday
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

41 Unix Next presentation… Vassilios alias UnixMan!!!

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