Hardware and communications Flashcards
What is HDD?
Hard disk drive:
- Main storage on a typical computer
- magnetic storage
- Used to store operating system/files
Advantages/ disadvantages of HDD?
Advantages:
- Very fast access - but comparably slower than SSD
- Data can be read from any part of hard disk drive
Disadvantages:
- Moving parts - Not suitable for mobile( it also generates too much heat)
- Problems when it fails and data is not backed up
- Fragile
What is a switch?
- Switches packets from one port to another
- When packet arrives switch determines the port on which the destination address exists
- Switches preform switching at MAC level rather than IP level
- When a packet arrives at a switch the switch looks at MAC address table (Routing table)
- MAC addresses are permanent and unique
-Initially switch doesn’t know which port specific device belongs to so sends out discovery packet to discover which port relates to which networked device
What is error detection?
Ensures packets arrive at destination without corruption
Parity Bits- Adding additional bits to make number of 1s even or odd depending on type of parity chosen
Echo - Packets are returned by destination then compared by sender
Checksum - Calculation preformed on packet, generating checksum sent with packet, it is repeated and the checksum compared.
What is a router?
- Routes to correct port
- Routers are used to connect different segments of LAN together and allow access to outside networks
- Preform routing on IP level rather than on MAC addresses
- A router ultimately has to deal with more devices than a switch
- Routers are necessary when connecting to ant WAN
What is the internet?
Internet -A world wide communications infrastructure of interconnected packet-switched networks.
These networks use standard TCP/IP
provides infrastructure to access range of information resources and services via the world wide web
Also provides infrastructure for email and file sharing
What is routing?
Determines the path each packet takes and ensures that packets are delivered to their destination as quickly as possible
- Each route is determined using routing table which stores the different paths
- These tables are constructed in the memory of network components
The best path is chosen by the lowest cost rate
What is packet switching?
- Allows packets to take independent routes through the network
- Each packet designs it’s own route based of which lines are available and how heavy current load is
- Packets may not arrive in order meaning extra processing must be used to reassemble the final message
- Each packet is labeled with an order number
- Much more resilient to failed links as if one route is brought down packets can independently find new route
- Bandwidth can be used more efficiently as no part of network is reserved
What is circuit switching?
- A path across a network is set up in advance and all packets are sent in order down the same path
- All packets on arrival will be in order
- If part of route is corrupted whole circuit will fail
- When a link fails a new circuit has to be set up before communication can continue
- Bandwidth can be wasted - once a connection is made no there device can use the circuit till it’s free again- can lead to slower services overall
Common use: Phone network
What is system software?
Allows control over software and hardware of computer
what is application software?
Software that allows the user to carry out a specific task
What is client-server structure?
- Clients connect to servers in order to access the services e.g file storage
- Servers are known as centralised computing, as services and processing power are held at a centralised point rather than distributed
- Makes use of request response model
What is peer-to-peer network?
- Each computer has the same status as others-no server
- One of most common uses is file sharing
- a file required by a number of peers is downloaded in parts by each peer
- Allows very large files to be downloaded efficiently
- Can be used to share processing load for complicated calculations
- Each peer solves part of problem and returns it to peer responsible for consolidating.
what are the protocols?
HTTP (Hypertext Transfer Protocol) - used fo transmission of webpages/webpage components
-Port 80
FTP(File transfer protocol) - Transmission of files
-Port 21
TCP(Transmission Control Protocol) - streamlike communication with error detection, ordering of packets and confirmation packet has been received
UDP(User datagram protocol) - Fire-and-forget approach with minimal protections
IP(Internet protocol) - network layer protocol that provides routing
What is OCR?
Optical character recognition:
-Converts printed media into editable tex documents using a scanner
-allows user to change text on a printed document
it also allows books to be digitised -used for e-readers
-Post processing step that occurs after a document has been scanned
-Preforms pattern matching by scanning for shapes it recognises as letters numbers or symbols
-This is done by comparing binary data to an internal database
-When binary shape is found OCR transforms it until it matches a known shape
-can get it wrong so document must be proof read
