Basics of computer Franck Theeten CABIN training, June 2013 Royal Museum for Central Africa, Tervuren

History 1937: Turing Machine: abstract representation of a computer (tape recorder) that can automatically solves any problem represented in its own alphabet (WWII) first computers (Z1, Mark I, ENIAC) Circa 1980: development of the personnal computer (IBM PC) Circa 1997: development of the INTERNET (via the HTTP protocols) Circa 2005: development of the smartphones

Source: Wikipedia 1: screen 2: motherboard (intenal) 3: Central Processing Unit 4: Random Access Memory 5: Expansion connectors 6: Power supply 7: CD Reader 8: Hard disk drive 9: keyboard 10: mouse

The Motherboard Processing the information No permanent storage RAM CPU Bus (exchange circuit) Hard disk drive RAM: Temporary copy of the information (closer from the CPU)

Binary (I) Assembly is the fundamental language of the CPU Only 2 signs: 0 and 1 2 operations: addition and substraction Computer doesn’t count on base 10 but on base 2 (binary)

Binary (II) BIT: basic storage unit (‘0’ or ‘1’) Byte: word of 8 bit (for signs) => => => => =>5

Binary (III) BIT: (‘0’ or ‘1’) Byte: word of 8 bits => basic storage unit

Binary (IV) => = => = =>?

Alphabetical characters (I) Everything has to be translated to binary numbers Including letters ans signs –ASCII: transposition table of 7 bits=> only 128 characters (non accented) –ASCII with extension (8 bits)=> 128 signs from ASCII extensions (codepages) for several alphabets (different extensions) –Compatibility problems between the extensions –Non european characters not taken into account

Alphabetical characters (II) –Unicode: transposition table of 2 bytes (255*255 characters = possibles characters) eg: ﻍ ♂♀  ĭ –UTF-8: unicode where the most current unaccented european characters are stored on 1 byte (win space!), the others characters on 2 bytes

Alphabetical characters (III) Note: The Windows notepad can easily convert documents from ascii to unicode o UTF-8 when clicking on « save as » Very useful for converting documents between software and platforms raw text documents only, not Word!.

Networks

Network : IP address A computer in a network is identified by an IP (‘Internet Protocol) address –32 bits/4 bytes : eg: bits range (IPv4) is becoming too small at global scale: IPv6 next protocol with 128 bits/8 bytes

Network : IP address How to know your own ip adress? Windows: –open «cmd » –write ‘ipconfig’ Linux: –open «shell » –write ‘ifconfig’

Networks : IP address

Networks : address resolving On the Internet, as an individual customer, you more than likely have a temporary IP adress DHCP (Dynamic Host Configuration Protocol) server: the service of a provider allocating and changing the IP address of a single station (average duration lease : 3 days)

Networks : address resolving Most of time you don’t use an IP address, but a « textual » HTTP address (Hyper text transfer protocol) to acces resource: e.g: Reponse:

Networks : address resolving page/cabin_call_2013 The Server address The first « / » The page on the server

Networks : address resolving The Server address

Networks : address resolving This server address actually corresponds to an IP address: The Server address

Networks : address resolving Inserting the IP in the browser also retrieves a page from the same server

Networks : address resolving Domain Name Server (‘DNS’): Service establishing the correspondance between the IP adress ( ) and the domain name adress m.be m.be

Networks: address resolving Resolving an adress: from right to left (global to specific) –.be => service in Belgium –.africamuseum.be => server at the Royal Museum for Central Africa –cybertaxonomy.africamuseum.be => website from the cybertaxonomy service –cabin.cybertaxonomy.africamuseum.be => cabin part of the cybertaxonomy website => Several cascading DNS servers are used (first a global one to get the domain of country: «..be », and finally an internal one for the service inside of the museum

Networks: address resolving Resolving an adress: by cascading DNS –.be –.africamuseum.be –cybertaxonomy.africamuseum.be –cabin.cybertaxonomy.africamuseum.be

Networks: DNS On the Internet, an institution having his own websites probably uses a permanent Internet Address and DNS entry (≠ individual temporary DHCP address) –Commercial service from the Internet Sevice Provider or address available from public authorities

Network:nslookup How to know the ip adress of a website? Windows: –open «cmd » –write ‘nslookup ’ Linux: –open «shell » –write ‘nslookup ’

Network: nslookup Example of ‘nslookup’ query

Network: Port A computer in a network is identified by an IP (‘Internet Protocol) address 32 bits/4 bytes : eg: A service in a computer is identified by a port number Eg. Port number for web page (enabled by default) Server adress

Network: port Port numbers, examples: – (web pages, can be omitted) – (FTP: service to directly uload or download files that can handle deconnection) – (secured FTP) – (MySQL database) –…

Network: firewall firewallA firewall –Can disallow network traffic from/to a specific IP address (to block a server) Domain (to block a domain) Port (to block a software) –Can disallow Incoming traffic to prevent the installation of malicious programs ( spyware; trojan, worms) Outgoing traffic (to prevent already installed viruses to dispatch information of infect others-