GCSE Computer Science: Data Representation

GCSE Computer Science: Data Representation

1. Image Data

   • Bitmap images are made of pixels
     • Pixel = Smallest identifiable area of an image
     • Each pixel = a single colour and given a binary number to identify it
       • Change the colour ➝ Change binary value
   • Resolution = Concentration of pixels in an area
     • Area is defined by image Width * Height
     • 72dpi (dots per inch) = screen resolution
     • 300dpi = print quality resolution
   • Metadata = Data about data (information that is stored with a file
     • Colour depth
     • Resolution
     • Date created
     • Author

2. Sound Data

   • Analogue sound signals are continuous
   • Digital sound signals are discrete
   • Sound is digitalized by repeatedly measuring and recording the sound wave
   • E.g. 2 second 6hz sound sample using 4 bits per sample
     • 2(seconds) * 6(hz) = 12
       • 12 * 4(bits per sample) = 48
         • 48 / 8(bits in a byte) = 6
           • Answer = 6 bytes
   • Recording quality improves the more frequently we sample the sound
     • & the more accurately we record the wave height

3. Binary

   • 1 bit = a single 1 or 0
   • 1 byte = 8 bits = 1 character of text
     • Capital and lower-cases have different values
   • 1KB = 1024 bytes
   • 1MB = 1024 KB or 1024*1024 bytes
   • 1GB = 1024 MB
   • 1TB = 1024 GB
   • Nibble = half a byte or 4 bits
   • 8 bits has 256 combinations
   • 4 bits has 16 combinations
   • 1 bit has 2 combinations
   • Adding binary
     • 0 + 0 = 0
     • 0 + 1 =1
     • 1 + 1 = 0 (Carry 1)
     • 1 + 1 + 1 = 1 (Carry 1)

4. Hexadecimal

   • 0-9, A-F (15 characters)
   • Hex to Denary = (Table) 16s | Units
     • Denary to Hex = [number] / 16
   • Binary to Hex = Split
     • Hex to Binary = add the split

5. Machine Code

   • E.g. TotalMark = mark + 20
     • TotalMark is a storage space
     • Loads mark and adds 20
   • Keeps repeating an instruction until it is told to stop

6. Binary Logic

   • Logic gate = A circuit that produces an output based on an input
   • Truth table = A method for recording all possible input combinations and determining the outputs
   • Logic circuit = A circuit made by lots of logic gates
   • Boolean algebra = Method for expressing mathematically a logic circuit

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