Monday, March 9, 2015

Is it valid or allowed, can check if something is valid but sometime inacurrate
You can check if it is not correct.
This ensure data is correctly inputted and spots human errors.
Ensures data entered complies with allowable data
many different types of validation include:

Range checks
format check
type character checks presence checks
Length checks
Lookup existence.

Is it the same?

Hesitance check
It is a number that is derived from the other contents of the number

Backing up and archivivng
full compies every file fully]
Incremental Backup
Only copies files that are changed in the last backup

not the same as backup

storing old/unused data

Taking it from server mainframe

Transferring onto storage medium

Unlikely to be used again but still available.

Syntax error

  • Missing extra brackets
  • Using variables
  • Brackets not used properly
  • The statement in the code does not follow the rules of the language.
  • Usually detected by the translator, as the statement cannot be understood.
  • Programs will not be compiled
Logic Error
  • The syntax of the code is correct
  • the code does not do what it should
  • Will usually run normally but with some unexpected result
  • Usually tested while being tested
  • Incorrect mathematical formulae
  • Misplaced brackets
  • Instruction written and therefore executed in the wrong order
Run time error
  • The syntax is correct
  • the logic of the program is correct
  • extreme circumstances cause crash
  • program attempts impossible operation
  • causes program to crash at run time
  • usually detected while testing
  • Division by zero
  • attempt to access non existent file
  • attempt to reference array elements before they are initialised 
Test Data
Data which syhold genarate an error message 

OSI Model

A set of rules that govern how something works.
Within a computer science:
  • A communication protocol is a system of digital rules for data exchange within or between computers
  • When data is exchanged through a computer network, the rules system is called a network protocol 
Logical Protocol (SMTP) - It is how emails are sent

  • HTTPS - Browsing through the net 

  • TSP

  • Bluetooth
  • Wifi
Lowest layer is logical and the highest is physical.

Physical layer = Describes electrical and physical specifications for devices: Cable, connectors, hubs.

Data link layer = Provides connections between hosts on the same network: Ethernet 

Network layer =  Provides connection between hosts on different networks :IPv4 and IPv6. Routing of packets.

Transport = Provides transport of data: TCP and UDP. End to end connections.

Session =  establishing a connection. Controls the dialogs between computers (handshake). Also controls duplexing termination and restarts. 

Presentation = compressing the data.  Provides a context for communication between layers 
ASCII Characters, Encryption and decryption. Compression.

Application = HTTPS, where we find network application eg mail, browser 
  • All
  • People
  • Studying
  • This 
  • Needs
  • Drastic
  • Psychotherapy

It hands communication between computers across networks.

Global and Local Variables


  • The scope of a declaration is the block of code where the identifier is valid for use

  • A global declaration is made outside the bodies of all function and outside the main program. it is normally grouped with the other global declarations and places at the beginning of the the program file.
  • Local declaration is one that is made inside the body of a function. locally declared variables cannot be accessed outside of the function they were declared in
  • It is possible to declare the same identifier name is different parts of the program.

Local Variables

  • We have used thus have been local variables
  • A Local variable is a variable which is either a variable declared within the function.
  • As you may have encountered in your programming if we declare variables in function then we can only use them within that function. This is a direct result of placing our declaration statements inside functions.

Global variable

  • A global variable def is a variable which is accessible in multiple scopes
  • It is important to note that global variables are only accessible after they have been declared.
  • Undisciplined use of global variables may lead to confusion and debugging difficulties.
  • Instead of using global variable in function, try passing local variables  by reference.

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.

Wednesday, January 7, 2015

Representation Of Data and Binary

All digital data are stores as binary. Eg Words, Cameras, Monitors...

When converting binary into decimals or reverse the left side is the most significant bit and the right side is the least significant bit.
8 bits = 1byte

BCD is when we code each part of the data by using a nibble.

By using Sign Magnitude method we loose a bit meaning the biggest number we can store is 127.

2a Complement
We assume that the MSB is a negative and the rest of the bit is positive adding to the negative number.

Three way of coding
EBCDIC is dead, stores data on a magnetic tape. cannot store keyboards characters.
ASCII every keyboard character is given a corresponding binary code. every letter is given a binary number.
UNICODE uses 2 bytes it is replacing ASCII it is used to cover more languages in the world, it is more important in the internet as it can store more languages.