Basics of computer
Franck TheetenCABIN 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
• 1941-1945 (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
RAM
RAM
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)
0 0 0 0 0 0 1 0 =>3
0 0 0 0 0 0 1 1 =>4
0 0 0 0 0 0 0 0 =>0
0 0 0 0 0 0 0 1 =>2
0 0 0 0 0 1 0 0 =>5
Binary (III)
• BIT: (‘0’ or ‘1’)• Byte: word of 8 bits => basic storage unit
1 1 1 1 1 1 1 1
1248163264128
Binary (IV)
1 1 1 1 1 1 1 1
1248163264128
1 1 1 1 1 1 1 1 =>128+64+32+16+8+4+2+1=255
0 0 1 0 1 0 1 1 =>32+8+2+1 =43
0 0 0 1 0 0 1 0 =>?
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 + 127 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 = 65 025 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: 255.255.255.0
192.168.0.1
• 32 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: http://cabin.cybertaxonomy.africamuseum.be/page/cabin_call_2013• Reponse:
Networks : address resolving
• http://cabin.cybertaxonomy.africamuseum.be/ page/cabin_call_2013
The Server
address
The first
« / »
The page on the server
Networks : address resolving
• http://cabin.cybertaxonomy.africamuseum.be/
The Server
address
Networks : address resolving
• http://cabin.cybertaxonomy.africamuseum.be
• This server address actually corresponds to an IP address: 193.190.223.52
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 (193.190.223.52)
and the domain name adress http://cabin.cybertaxonomy.africamuseum.be
Networks: address resolving• http://cabin.cybertaxonomy.africamuseum.be
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 resolvingResolving 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 <adress of the website>’
• Linux: – open «shell »– write ‘nslookup <adress of the website>’
Network: nslookupExample of ‘nslookup’ query
Network: Port
• A computer in a network is identified by an IP (‘Internet Protocol) address
• 32 bits/4 bytes : eg: 255.255.255.0• A service in a computer is identified by a port
number • Eg. http://193.190.223.52:80
Port number for web page (enabled by default)
Server adress
Network: port
Port numbers, examples:– http://193.190.223.52:80 (web pages, can be
omitted)– http://193.190.223.52:16 (FTP: service to directly
uload or download files that can handle deconnection)
– http://193.190.223.52:22 (secured FTP)– http://193.190.223.52:3306 (MySQL database)– …
Network: firewall
• A firewallfirewall– 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-
