Hardware and Software

Hardware - Electronic parts of a computer - Processor, Input and Output devices.
Software - Data which runs on the hardware - Programs

Software - System Software - Operation Systems - Operate the Hardware. e.g. Windows, MAC, Linux
                                            - Library Programs - Common Functions.
                                            - Utility Programs - Specific tasks.
                                            - Translators - Turns higher level language into machine code.
               - Application Software - General Purpose - Can be used for a number of tasks.
                                                   - Special Purpose - Supports one specific task.
                                                   - Bespoke - Software that is tailored.

Ports

HTTP - (Web Browser) Port 80
HTTPS - (Web Browser (Safe)) Port 443
FTP - (File Transfer) Port 20
SMTP - (Sending E-mail) Port 25
POP3 - (Receiving E-mail) Port 110

TCP/IP Stack

TCP - Transport Control Protocol - Breaks data down into packets.
IP - Finds a computer on a network to route the packets of data to.

Layer 1 - Application Layer - Specific networking applications e.g. web browser, word processor
Layer 2 - Transport Layer - Breaks data down into packets and adds a sequence number to each packet, also adds source and destination ports.
Layer 3 - Network Layer - Adds the source IP address and the destination IP address to the packets.
Layer 4 - Link Layer - Adds source and host hardware addresses and puts packets on the cable.

Host Hardware - Media Access Control (MAC)

End of Topic Assignment - The Internet

Before leaving work Bob logs onto his work computer. He uses the intranet, a part of the internet that is used only for businesses, to look up some information of a colleague. He uses a simple mail transfer protocol, SMTP, to send them an e-mail containing a link on the extranet; it is sent to the staff only e-mail notice board.

                Bob then goes home, meanwhile after the e-mail had been sent the transport layer (TCP Layer) this is where the e-mail is broken down into packets of data and adds the source and destination ports to the packets as well as the sequence number; that way if a packet gets there quicker than another packet that was before it then the packets will be placed back in order. Then it goes to the network layer also known as the IP Layer, this is where the source and destination IP addresses are added, this is so the packet knows where to be delivered to. After the IP Layer the link layer adds the hardware addresses to each packet, the hardware addresses are also known as MAC Addresses, and puts them on the cable.

                At home Bob uses his internet service provider to access the web. He uses this is access the Amazon webpage, using the HTTP protocol. The request is from the client to the host server. The client requests the web page from the application layer and the moves it way down the TCP Layer which adds a port number, which will be port 80 due to it being a web page, it will also add the sequence number to the packet of data that it has been split into. The packet is then passed to the IP layer where the source IP address is and where the destination IP address is. The packet is then once again passed down to the link layer where the MAC address is added so that the packet is added to the cable, for it to be sent. The packet is now sent across the local area network, which is a network that computers and other servers use to relay information. The local router for this local area network reads the address that the packet has and routes it to the right destination. When the packet arrives at the client server it goes up the layers back to the application layer. At the network layer the IP addresses are removed and then the transport layer reconstructs the data to be looked at on the application layer, which in this case is the web page Amazon. The web page is shown in the internet, which is a network of networks that allows a number of computers to gain information from other computers around the world. The packets have to make their way through the firewall to get to the web browser to show the page. The firewall stops untrusted data from gaining access to your computer and your files. You’re home network works like a sort of intranet as it only allows you to gain access to files and information on that network but also allows you to access information on the extranet.  The packets that bob has sent will be processed to be directed to port 80 which is where all web pages are sent. Once the web page has been found the data is sent back along the path (through all the layers in the TCP/IP stack) back to the client (Bob). Bob buys a present for Alice on the Amazon website, he then uses the POP3 protocol to check for any new mail, POP3 is used for receiving e-mails and SMPT is used for sending e-mails, after checking for new e-mails he sends Alice an e-mail about the present, this will then go through all the layers and through port 25 which is the standard e-mailing port.

Useful Definitions

Packets - part of a large piece of information
             - Contains three parts - Header - Senders IP Address
                                                              - Recievers IP Address
                                                              - Protocal (HTTP)
                                                              - Packet Number
                                               - Payload - The Actual Data
                                               - Trailer - Data to show the end of the Packet
                                                            - Error Corrections

Router - a specialised piece of computer equipment which recieves and sends packets, the router recieves the packet and then forwards them onto the right computer.

Domain Name - Easily Recognised and easy to remember
                       - Example - www.google.com

Protocol - Specifies what path the computer should follow to access the requested file.
Domain - Points to the website where the file is.
Path - The route the internet takes to get to the file being requested.
File Name - The name of the file.

IP Address - a unique number allocated to every computer
                  - Made up of 4 sets of 3 digit numbers (86.134.238.10)

Domain Name Server (DNS) - Translates IP addresses into recognizable domains.

Internet Registries and Registras - Registries - Number
                                                 - Registras - Name
                                                 - Manages IP Addresses and Domain Names

Internet Service Provider (ISP) - Provides an entrance to the internet.

Intranet - a closed off portion of the internet within a single location for example within a business.
Extranet - a piece of an organisations intranet which has been made securely available to other oganisations or individuals.

Clients - Main job is to recieve information. It is a computer on a network using resources provided by the server.
Servers - Main job is to send information. It is a computer on a network that provides resources for clients.

URI - Uniform Resource Identifier - Provides a unique ID
URN - Unique Resource Name - The unique name for something e.g. isbn numbers.
URL - Uniform Resource Locator - Unique location of something e.g. website address.

Program Control Unit (PCU) - Fetches programs from memory and executes them one at a time.
Arithmetic and Logic Unit (ALU) - Performs logical operations when instructed by programs.
Registers - Fast memory locations within the processor.
System Clock - Sends out ticks to sync the operation of the components (measured in GHz)
Internal Bus - Buses within the processor which alllow the PCU & ALU to communicate.
Dedicated Registers - Assigned a specific purpose by the designer of the processor.
General Purpose Register - Available for the programmer to store data temporarily.
Accumulator (ACC) - Holds the result of calculations.