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-