Transcript Basics of computer - Royal Museum for Central Africa

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
• 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
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
Source: Wikipedia
The Motherboard
• Processing the information
• No permanent storage
RAM
Hard
disk drive
RAM
CPU
RAM
RAM
RAM:
Temporary copy of the
information
(closer from the CPU)
Bus
(exchange circuit)
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 0 0
=>0
0 0 0 0 0 0 0 1
=>2
0 0 0 0 0 0 1 0
=>3
0 0 0 0 0 0 1 1
=>4
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
128
64
32
16
8
4
2
1
Binary (IV)
1 1 1 1 1 1 1 1
128
64
32
16
8
4
2
1
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
0 0 0 1 0 0 1 0
=>?
=43
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
The
Server
address
• This server address actually corresponds to an IP address:
193.190.223.52
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.africamuseu
m.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 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 <adress of the website>’
• Linux:
– open «shell »
– write ‘nslookup <adress of the website>’
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: 255.255.255.0
• A service in a computer is identified by a port
number
• Eg. http://193.190.223.52:80
Server adress
Port number for web page
(enabled by default)
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 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-