Computing

• CPU components

  Control unit

  ALU

  Cache

  Registers
• Control Unit

  • controls flow of data inside CPU
  • controls and monitors hardware attached to the system
  • provides timing signals and contains decoder
• Registers

  tiny, super fast pieces of onboard memory each with its own purpose and temporarily holds data
• Factors affecting CPU

  • Cache size
  • Number of cores
  • Clock speed
• Number of cores

  • more cores mean more instructions executed.
  • CPU with multiple cores have abiltity to run more prgrams at the same time as they have more power.
  • However, these have to communicate with each other so slows performance
• VM Architecture


  Program counter

  MAR

  MDR

  Accumulator
• MAR

  • holds address of where current data is to be fetched or stored
  • contents of PC are copied here
• MDR

  • where data from MAR is placed after fetched
• Primary storage

  • needs power
  • holds instructions needed by the computer while running
  • relatively small storage capacity in comparison to secondary
  • faster access time to than secondary
• Secondary storage

  • non volatile
  • needed for backup and archive of files
  • needed for storage of programs and data when no power available
• More RAM

  • less use of virtual memory which slows performance as it is a form of secondary storage so needs to be moved back to RAM when needed
  • more programs can be open at once without affecting performance
• BIOS

  • stored in ROM and loads OS
  • performs self-diagnostics on hardware
  • provides basic user interface
• Switches connect computers , use MAC address and records the address of where accessed

  Routers connect networks, use IP address and stores address of devices attached
• Summary

  websites are hosted on webservers

  your website/webserver has an IP address

  your browser sends URL to a DNS

  DNS has a linked IP address and finds it

  If it cannot be found, the request is passed to another DNS

  IP address is sent back to browser/computer

  Browser sends request to webserver

  Web server sends request and sends the webpage/file/data to user
• Star topology

  Each computer is connected to a switch/hub using their own cables. The hub is connected to a server. The server controls the network
• Star advan


  Data is only directed to the intended computer directly

  Consistent performance even when the network is heavily use .

  If one link fails, all the other devices will continue to operate

  Easy to add new devices without disrupting the network

  Fewer data collisions
• Star disadvan

  • Requires additional hardware such as the central switch
  • If the central device fails the whole network goes down
  • Lots of cabling required which can be costly
• Mesh topology

  Each computer is connected to all the other computers in the network. This is very similar to peer-to peer networking

  In partial mesh, each computer is connected to some others
• Mesh disadv

  • Expensive to install cabling if using wired connections
  • Network maintenance and administration is difficult
• Network standard


  -A set of agreed requirements for hardware and software

  -These are important as they allow manufacturers to create products and programs that will be compatible with products and programs from other manufacturers
• Network Protocols


  A set of rules for how devices communicate with each other and how data is transmitted across a network
• IPv4


  Uses 32 bits to store the unique address
• IPv6


  Uses 128 bits to store the unique address

  IPv6 was created due to the increasing number of devices that need unique IP addresses
• MAC Addressing

  -MAC address is assigned to each network enabled device by the manufacturer (on the network Interface Card).

  -Every networked device in the world has a unique MAC address

  -MAC addresses cannot be changed unlike IP addresses

  -When you connect to a network, you are connecting to a local area network and you send and receive data through a MAC address.
• • Inside a LAN, data is sent in packets and directed by switches using MAC addresses.
  • Between networks, data is sent in packets and directed by routers using IP addresses
• TCP/IP protocol

  -This is a set of protocols which dictates how data is sent between networks

  -TCP breaks up data into small packets of data and sends it over a network

  -Once it reaches the destination, it reassembles the packets

  -It checks if the transmission of data was successful and if it has any errors

  -It resends lost messages

  -IPs are responsible for directing packets to their destination over a WAN( Internet)
• HTTP (Hypertext Transfer Protocol)


  -provides the rules that your web browser and web server follow when requesting and supplying information

  -used for sending requests from client to server and returning web content from web server back to web client
• HTTPS ( HyperText Transfer Protocol Secure)


  -encrypt the information so it cannot be understood if intercepted
• FTP (File Transfer Protocol)


  -provides the rules for file transfer between devices

  -The rules include editing, accessing and moving files between a client and server and vice versa

  -Specifically designed to transfer large files
• POP (Post Office Protocol)


  -a way of retrieving an email and deleting the email from the server after it has downloaded the entire message to your local device

  -This means that the email can be only read from that device since it has been saved to that device
• IMAP (Internet Message Access Protocol)


  -way of retrieving protocol to fetch a message of data and attachments

  -It keeps the emails on the mail server- you only download a copy

  -This means you can view your emails from any internet enabled device
• SMTP (Simple Mail Transfer Protocol)


  -an email protocol used for sending emails

  -transfers emails between email servers to send/transmit the email
• Layers

  -All data must pass through each layer

  -Application (HTTP, FTP, SMTP, POP, IMAP)

  -Transport (TCP)

  -Internet (IP)

  -Network (Ethernet, WiFi)
• Advan of layers

  Each layer can be changed/altered without affecting the other layer

  It breaks the network communication into manageable pieces

  Each layer has its purpose so it does not need to consider what the other layers do
• Decomposition 


  Decomposition involves breaking down a complex problem into smaller sub-problems. These smaller sub-problems are easier to

  understand and solve
• Abstraction 


  Abstraction involves disregarding unnecessary detail from a problem so that the main processes can be more easily focused on
• Syntax Error


  Mistakes in the way that the code is written. They do not follow the rules of the language used
• Logic Error


  Bug in a program that causes it to operate incorrectly, but not to terminate or crash. Produces unintended or undesired output
• High Level  Language


  A programming language which is close to English in the commands used making it easier to learn and understand.
• Low Level  Language

  A programming language closer to machine code.They are

  tricky for humans to read and write but are easier and quicker for a computer to run