Thursday, February 26, 2015

Mock Exam What I need to do next?

1) Alway add two key points, eg 'State two differences between ROM and RAM'

2) Use correct key words.

3) Use correct spelling when answering long questions.

4) Write workings out in the order of workings.

5) When describing an output, explain why it would be used for the SITUATION required.

6) Keep it simple, don't waffle.

7) Use the marks as a guideline of how many points I should include.

8) Learn basics keywords (sequences, iteration, statement)

9) Learn the different types of testing

10) Need to use the information to help answer the question.

11) 4 mark question, State, 'example', 'explantation'.

12) Follow the code when trying to solve something.

Wednesday, February 25, 2015

Data Transmission

What is a network?
A network is collection of two oar more computers connected together to share resources.

LAN: Covers a small geographical area eg a single building in school.

WAN: Covers a large geographical area for example a country or continent.

To build a network:

  • at least 2 computers 
  • a network card 
  • network cable 
  • a switch or a hub to connect the cable to and exchange signals 
  • on large networks with a significant amount of traffic a network server is needed to mange data transmission. 
Serial and parallel
Bits are sent one at a time over a single wire. The speed of transmission depends on the medium being used but could be very high (in some cases faster than a slow parallel transmission).

Parallel transmission is used inside computer systems and for very short distances. A parallel port could send 8, 16 or 32 bits simultaneously down separate lines. Before USB used to connect to printers.

Is used for transmission of data in one direction eg from a mouse to a computer

Used to transmit data in both directions but not at the same time.

duplex modes
Is used for transmission of data in both direction simultaneously.

Bit rat
The number of bits transmitted each second or the rate at which data is transferred.

Different bit rates are suitable for different applications. Largely based on how time sensitive the information is.

Video streaming -  requires a high bit rate as there is lots of data and any delay will interrupt the video

Transferring word documents - Can use a lower bit rate as the files are needed on real time and people can wait a few min for the files to arrive.

Errors in data transmission
Its very easy for data to become corrupted during transmission. There are three main ways that computers check for errors in data.

Echoing - back The receiver sends the data back to the sender who checks that it matches what was originally sent.

Check sums - Extra digits or numbers are added to the end of a complex sequence. These numbers are calculated based on the number in the sequences. When the sequence in received the check number ins recalculated and if it doesn't match then the data is resent.

Parity check - 1 bit in each byte is reserved as the parity bit. The parity bit is 1 if the number of 1s in the rest of the byte is add 0 if the number of 1s is even.

Packets - When data is transmitted across a network the whole file is not sent at once. the files is broken up into a smaller chunks called packets and these are transmitted separately across the network.

Once a file has been broken up in to packets each packet has a header added to it, this contains information like the packets sender, destination, size and the protocol it it using.

Transmitting data in packets instead of whole files is more reliable and more secure.

Circuit switching - all the packets take the same route to their destination
This means that it is quick to assemble packets at the receiving end as they arrive in the order they were sent.

Packet switching - All the packets take different routes to their destination. This means that it takes longer to assemble packets at the receiving end as they dont arranging the order they were sent. However packets can also avoid slower areas of the network to avoid overloading the network.

Peer to peer - making connection to together computers with equivalent class with your network.