paper 2

• Binary


  The simplest numbering system, easy to represent with switches
• Bit


  A binary unit, a 0 or 1
• Byte


  8 bits
• Kilobyte, Megabyte, Gigabyte, Terabyte


  Each one a thousand times the previous term
• For hexadecimal, digits 0 to 9 are the same as decimal, 10 to 15 use letters A to F
• Purpose of hexadecimal


  To shorten binary, one hex digit equals four binary digits
• Binary addition


  Approach like normal maths, lay out in columns
• Binary shift


  Multiply by 2 (left shift) or divide by 2 (right shift)
• Right shift rounds the number down
• Big areas in data representation

  • Characters (letters, numbers, symbols)
  • Bitmap images
  • Sound digitisation
  • Data compression
• Character set


  A table of character codes
• ASCII


  Allocates 7 bits per character, only 128 characters
• Unicode


  Longer character codes, can represent thousands of characters and languages
• Bitmap image


  An image of pixels, pixel is the smallest dot of colour
• Image size


  Width x Height
• Color depth


  Number of bits per pixel, not number of colors
• File size for images

  Image size x Color depth
• Analog sound


  Continuous and smooth, can't be used in a computer
• Digitising sound


  Sampling the amplitude at regular time intervals, sampling rate is samples per second
• Sample resolution


  Number of bits per sample, like color depth for sound
• File size for sound


  Sampling rate x Sample resolution x Duration
• Compression


  Reducing file size to take up less storage and shorten upload/download times
• Lossy compression


  Deletes part of the file permanently, suitable for images and sound
• Lossless compression


  Rearranges the file to store it more efficiently, no data lost, for documents and programs
• Huffman coding


  Lossless compression that gives frequent characters shorter codes
• Run-length encoding


  Lossless compression that stores data in frequency-value pairs
• Boolean operators


  • NOT
  • AND
  • OR
  • XOR
• NOT gate


  Flips the input, 0 becomes 1 and 1 becomes 0
• AND gate


  Output is true only when both inputs are true
• OR gate


  Output is true when either or both inputs are true
• XOR gate


  Output is true when either but not both inputs are true
• Software categories


  • Application software
  • System software
• Application software


  Aimed at end users, carries out tasks
• System software


  Supports the running of the computer system, includes operating systems and utilities
• Operating system


  Manages the hardware and other programs on the computer
• Input/output devices


  Devices plugged into the computer, require drivers to work with the OS
• Programming language types


  • High-level
  • Low-level
• High-level languages


  Written in English-like syntax, portable across platforms, slower to run
• Low-level languages


  Assembly and machine code, closer to what the CPU is doing, faster to run but not portable
• Assembler


  Translates assembly language to machine code, one-to-one correspondence