2.6 DATA REPRESENTATION

2.6 DATA REPRESENTATION

1. Storage

   • BIT
     • NIBBLE
       • BYTE
         • KILOBYTE
           • MEGABYTE
             • GIGABYTE
               • TERABYTE
                 • PETABYTE

2. DENARY(DECIMAL)

   • A way of representing a number using numbers from 0-9. This is called Base 10 notation because there are 10 possible numbers (012345678&9)
   • Hexadecimal
     • A way of representing a number using numbers from 0-9 and A-Z. This is called Base 16 notation because there are 16 possible numbers (0123456789ABCDE&F)
     • Hex Character
       • A singular Hexadecimal character. E.g D3 is made up of the characters 'D' and '3'

3. BINARY

   • A way of representing a number using only 0s and 1s. This is called Base 2 notation because there are only 2 possible numbers (0&1)
   • HOW BINARY IS USED TO REPRESENT DATA
     • Computers are made up of logic circuits which use 1 and 0 to show high and low voltage
   • OVERFLOW ERROR
     • Where the binary number is too big to fit into 8 bits
   • UNDERFLOW ERROR
     • Where the right 1 falls off the right side of the byte
   • BINARY
     • BINARY SHIFT
       • A fast method of multiplying and dividing a binary number by a power of 2. All bits are shifted to the left or right.
     • LEFT SHIFT
       • Where all the bits move to the left. The remaining bits are filled with 0. This has the effect of multiplying by 2.
     • RIGHT SHIFT
       • Where all the bits move to the right. The remaining bits are filled with 1. This has the effect of dividing by 2.

4. Check digit

   • A digit added to the end of a string of numbers to check that data has been received correctly
   • Even parity bit
     • This parity bit is added to make a binary string have an even number of 1s e.g. 1010001 needs another 1 added to make it even
   • Odd parity bit
     • This parity bit is added to make a binary string have an odd number of 1s 1010001 needs a 0 added because it already has odd number of 1s

5. Bases

   • Base 2
     • A number system that uses 2 possible numbers (0&1)
   • Base 10
     • A number system that uses 10 possible numbers (012345678&9)
   • Base 16
     • A number system that uses 16 possible numbers (0123456789ABCDE&F)

6. Character

   • A singular letter, number or symbol. E.g 'A','a','7','!'
   • Character set
     • This refers to the amount of characters that a computer recognises.

7. ASCII

   • The most commonly used character set in the English speaking world. Each character is given a 7 bit binary code (therefore can only store 128 characters).

8. Unicode

   • Tries to cover every possible character that might be written. The most common forms are 16-bit (65,536) and 32-bit (4,294,967,296) versions. It covers Greek, Russian and Chinese too!

9. Pixel

   • The squares that make up an image. The word stands for 'picture element'

10. Metadata

    • Means 'data about data'. This sounds confusing, but you could also think of it as 'properties' (e.g Resolution, Width, Height, Colour depth etc)

11. Colour depth

    • Refers to how many bits are used to store the colour of each pixel. E.g 2-bit colour depth gives 4 possible colours 00,01,10,11

12. Resolution

    • Refers to the density of pixels in an image (i.e how many pixels are within a certain area). It is measured in dots per inch (dpi)

13. Sample

    • Taking a snapshot of the wave at regular intervals (how many times this happens a second is called the sampling rate)
    • Sample size
      • Refers to how many bits can be used for each sample. 3 bits means that 8 possible 'levels' (voltages) can be represented. Of course, the more levels you have, the better the quality of the sound. The bit depth on CD is 16 bits. On DVD is 24 bits.
    • Sample frequency
      • Refers to how many samples you take in a second. It's usually measured in kilohertz (kHz). A common frequency used in MP3s is 44.1 kHz (i.e 44,100 samples per second)

14. Bit rate

    • Refers to the number of bits used per second of audio. It's calculated using the formula Bit rate = Sampling frequency x Sample size

15. Digital

    • Analogue
      • A continually varying wave. It has to be converted into a digital signal for the computer to be able to process it
    • Can be represented by binary i.e. 1's and 0's

16. File compression

    • Reducing the size of a file (how much storage memory it takes up)
    • Lossy compression
      • A form of compression where some data is lost when compressing the data. You cannot get back the data afterwards.
      • Lossless compresion
        • A form of compression where a special algorithm is used to make the file size smaller but no data is lost (hence the term loss-less).

17. Logic gate

    • A special circuit that allows a specific output depending on the inputs. A processor is made up of millions of these circuits.
    • Logic Diagram
      • A diagram that shows how logic gates are connected together
    • AND Gate
      • A logic gate that has two inputs. If both inputs are '1' it will output '1', otherwise it will output '0'. It looks like a capital 'D'
      • OR Gate
        • A logic gate that has two inputs. If either or both of the two inputs is '1', its output is '1'. It looks like a curved triangle.
        • NOT Gate
          • A logic gate that has one input. If the input is '0', its output is '1'. If the input is '1', its output is '0'. It looks like a triangle.
    • Truth table
      • A table used to show the combinations for all the possible inputs and outputs of a logic diagram