9. File Size

• 1 nibble is how many bits , what is its number range?


  one nibble is 4 bits , its number range is 0-15
• 1 byte is how many bits , what is its number range?


  1 byte is equal to 8 bits. The number range of 1 byte is from 0 to 255.
• 2 bytes is how many bits , what is its number range?

  2 bytes is 16 bits, number range is 0 to 655,36
• 4 bytes is how many bits , number range?

  4 bytes is 32 bits , more than 4 billion is number range
• Characters are the letters and other symbols you can type on a keyboard

  Text data is made of characters. Text can be held in digital form and to do this each character is given a code number
• Two common character sets?


  ASCII and UNICODE
• What is a character set?


  The name for the set of characters and their code numbers
• Character sets are logically ordered

  In ASCII , B is 66 so what are A and Cs code number?

  A=65

  C=67
• three features of ASCII?

  -Fewer than 255 codes

  -Each code takes 1 byte

  -Only includes basic keyboard characters
• three features of UNICODE?

  -many thousands of codes

  -each code takes between one and four bytes

  -has all global alphabets , symbols , emojis and so n
• Kilobyte = KB , size is 1000 bytes

  Megabyte = MB , size is 1000KB

  Gigabyte = GB , size is 1000MB

  Terabyte = TB , size is 1000GB

  Petabyte = PB , size is 1000 TB

  To convert between units either divide or multiply by 1000
• Convert 4000KB to MB?

  4000/1000 = 4MB
• Convert 1.25MB to KB?

  1.25 * 1000 = 1250KB
• How to calculate text size?

  number of characters * bits per character
• How to calculate image size?


  number of pixels * colour depth
• How to calculate sound size?


  number of seconds * sample rate in hertz * bit depth
• Find the file size of a text file that is 500 characters long with 16 bits per character in kilobytes?

  no characters * bits per character

  500 * 16 = 8000bits = 1000 bytes = 1KB
• Find the file size of an image that is 200x300 pixels and has colour depth of 16 bits ? answer in KB

  (200*300) * 16 = 960,000 bits = 120,000 bytes = 120KB
• Find the file size of a 2 minute audio file with sample rate of 44.1kHz and a bit depth of 16 ? answer in MB

  number of seconds * sample rate in herts * bit depth =

  120 * 44100 * 16 = 84,672,000 bits = 10,584,000 bytes = 10.6MB
• Two types of compression?


  Lossy and lossless
• What is lossy compression?


  Permanently removes data from the file and limits the number of bits the file needs reducing the size
• Pros and cons of lossy compression?

  Pros:Takes up less bandwidth so files can be downloaded,streamed more quicklyCommonly used so lots of software can read lossy files

  Greatly reduces file size , meaning more files can be stored

  Cons:

  Loses data - file can't be turned back into originalCan't be used on text or software files as these need to retain all the information of the originalWorse quality than original , quality loss is usually unnoticeable
• What is lossless compression?

  Makes the file smaller by temporarily removing data to store the file and then restores it to its original state when opened.
• Pros and cons of lossless compression?

  Pros:

  No reduction in quality as data is removed temporarily

  Can be decompressed (turned back into orginal)

  Can be used on text and software files

  Cons:

  Slight reduction in file size so still takes up a lot of spaceLess effective than lossy compression at reducing size
• Examples of files using lossy compression?

  MP3 (audio)AAC (audio)JPEG (image)
• 3 Examples of files using lossless compression?

  FLAC (audio)TIFF (image)PNG (image