Computing GCSE

• Sampling Rate


  Samples taken per second (Hz)
• Sample Resolution

  Number of bits stored per sample
• Sound file size

  Rate (Hz) * Resolution (bits) * Duration (secs)
• Colour Depth


  Number of bits to store colour of each pixel
• ASCII


  7 bits per character ($2^7$)
• Unicode


  16 bits per character ($2^1$$^6$)
• Image file size


  Colour Depth * Width * Length
• Text file size


  Bits per character * Characters
• Hexadecimal Conversion

  Find the decimal for each half of the binary (A = 10...)
• Arithmetic


  0+0 = 0

  0+1 = 1

  1+1 = 0 carry 1

  1+1+1 = 1 carry 1
• Binary Shift


  Left shift 1 = x2

  Right shift 3 = /8
• Run Length Encoding


  Number of times value occurs + Value
• Huffman (Trees)


  Follow path down to desired character. Common characters have shorter code.
• Local variable


  Declared & exists/accessible only in Subroutines
• Global variable


  Declared & accessible throughout (including Subroutines)
• Records


  Group values of different data types
• Multiple Tables


  SELECT Field1, Field2

  FROM Table1, Table2

  WHERE Table1.ForeignKey = Table2.ForeignKey
• Logic Gates


  AND, OR, NOT, XOR

  
• Flowcharts


  ^-^

  
• Char-Code Conversion

  Character -> ASCII
• Substring


  Specific part of a string
• Function vs. Procedure


  Function: returns value to main program

  Procedure: does not
• Boundary, Erroneous Test


  Boundary: at the poles of what is(n't) accepted

  Erroneous: invalid
• UPDATE...SET

  UPDATE TableName

  SET Field = "x"

  WHERE Condition