2.6 - Data Representation

2.6 - Data Representation

1. How is data represented?

   • Bit = 0 or 1.
   • Nibble = 4 bits.
   • Byte = 8 bits/ 2 nibbles.
   • Kilobyte = 1000 bits.
   • Megabyte = 1000 KB
   • Gigabyte - 1000 MB
   • Terabyte = 1000 GB
   • Petabyte = 1000 TB

2. Denary --> Hex

   • Divide by 16 - Whole number = the first digit, the remainder = second digit.
     • 167/16 = 10.7
       • 10 = A, 7
         • Therefore 167 = A7

3. Binary ---> Hex

   • Split the byte into 2 nibbles.
     • Add up each number per nibble and get 2 digits. This is your answer.
   • You would tend to use hex because:
     • Has a shorter string so uses less storage.
     • Easily converted to binary if needed.
     • Programmers find it easier to work with.

4. Characters

   • ASCII has 7 bits.
   • Extended ASCII has 8 bits.
     • 256 possible characters.
   • Unicode has 2 bytes.
     • giving 2^16 possibilities (65,536).
   • To get the lower case version of a capital letter in binary, just add 32.

5. Images

   • Bitmap
     • Becomes blurred when you zoom in because each pixel is assigned a colour.
     • The page is divided into an invisible grid.
     • Every bit is mapped.
   • Vector
     • Follows a set of mathematical instructions.
     • For example:
       • Draw a circle, radius = 6 pixels, centre(10,10), line thickness =1 pixel.
     • Doesn't blur when zoomed in.
   • Each image holds 'metadata' - data about data.
   • Resolution - the number of pixels used.
     • The higher the resolution, the greater the quality.
     • The greater the resolution, the larger the size.

6. Compression

   • Saves space, reduces the amount of data transferred and runs quicker.
   • Lossless
     • No data lost, the reconstructed file is identical to the original and not all files can be compressed like this.
   • Lossy
     • Loses some info, acceptable to do this with images and vide0, but not text.

7. Audio

   • Sample frequency - the number of captured samples per second.
   • Sample size/Sample depth - the number of bits available per second.
   • Bit rate - the number of bits used per second.
   • More samples lead to better quality but larger file size.