Data Representation

• Units of size

  A) Bit

  B) Megabyte

  C) Gigabyte

  D) 1000 bytes

  E) 1000 gigabytes

  F) GB

  G) B

  
• The order of size goes; bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte, petabyte
• Denary: Base 10 number system that is our standard number system that goes from 0-9.
• Binary is a base 2 number system that only uses 0 and 1, used to represent the computers language.
• Binary Table

  A) 128

  B) 64

  C) 32

  D) 16

  E) 8

  F) 4

  G) 2

  H) 1

  
• Binary Addition Rules

  • 0 + 0 = 0
  • 1 + 0 = 1
  • 0 + 1 = 1
  • 1 + 1 = 0 (1)
  • 1 + 1 + (1) = 1 (1)
• Binary Shifts

  • used to multiply or divide by 2.
  • gaps at the beginning or end filled with 0s.
  • direction indicates whether it multiplies or divides the binary number.
• Left shifts multiplies a binary number. For every shift left, the number is doubled.

  Example:

  Perform a 3 place left shift on the 8 bit binary number 00101001.

  0 0 1 0 1 0 0 1

  0 0 1 0 1 0 0 1 0 0 0

  NOTE: If number is greater than 8 bits, then digits will overflow.
• Right shifts divides a binary number. For every place shifted right, the number is halved.

  Example:

  Perform a 2 place right shift on the binary number 00111100.

  0 0 1 1 1 1 0 0

  0 0 0 0 1 1 1 1

  NOTE: Answers with a right shift are similar to using the DIV function; remainders aren't taken into account.
• Hexadecimal Numbers

  • uses 16 digits.
  • 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
  • A (10), B (11), C (12), D (13), E (14), F (15)
• Characters

  • ASCII is the most commonly used character set in the English speaking world. Each ASCII character has a 7bit binary code totalling 128 characters.
  • The codes for numbers, uppercase, and lowercase are ordered ascendingly.
• Unicode

  • Tries to cover every possible letter or symbol.
  • Covers all major languages.
  • First 128 codes in Unicode are the same as ASCII.
• Formula for size of a text file using this formula.

  File size (in bits) = number of bits per character * number of characters.
• Storing Images

  • Images stored as a series.
  • Most images are bitmap images created using pixels.
  • Colour of each pixel is represented by a binary code. Number related to the number of bits the code has.
  • 2-bit images can make 4 colours.
  • You can make a greater range of shade and colour by increasing the number of bits for each pixel.
• Increasing colour depth and resolution increases the file size.
• Colour Depth: Number of bits used for each pixel.
• Total Number of Colours= $2^n$
• Resolution: Number of pixels in the image.

  Higher the resolution, more pixels is made up of, clearer the image.
• File size (in bits) = image resolution * colour depth = width * height * colour depth.
• Using more bits in an image, increases the file size.
• Metadata is the data about the data.

  • Includes file format, height, width, colour depth and resolution.
• Without metadata, devices wouldn't be able to display the images on screen as intended.
• Storing Sound

  • Sound is recorded by a microphone as an analogue signal.
  • Analogue signals need to be converted into digital data so that computers can read and store sound files.
  • Process is called smapling.
• Sample Rate: How many samples are taken per second. Measured in Hertz (Hz) or kilohertz (kHz).
• Bit Depth: Number of bits available for each sample.
• Calculating size of a sound file


  File Size (in bits) = Sample Rate (in Hz) * bit depth * length (in sec)
• Increasing the sample rate, means analogue recording is sampled more often, it will be better quality.
• Increasing the bit depth means the digital file picks up quieter sounds, closer to quality of the original recording.
• Increasing sample rate and/or bit depth increases the file size.
• Compression

  • Data Compression: When we make file sizes smaller, while trying to make the compressed file as close to the original as possible.
  • Has many uses; take up less storage, streaming and downloading as they take up less bandwidth, allows web pages to be opened faster.
• Lossy vs Lossless Compression

  Pros, Cons and Examples

  A) Lossy

  B) Lossless

  C) bandwidth

  D) loses

  E) all of

  F) quality

  G) temporarily

  H) decompressed

  I) reduction

  J) storage

  K) PNG

  L) MP3