Computing Topic 2

• What is the difference between Primary & Secondary storage?

  Primary:

  • Very quick as its directly accessed by CPU
  • Smaller storage size
  • Main memory
  • Includes RAM & ROM

  Secondary:

  • Slower as its not directly accessed by CPU
  • Larger storage size
  • Long term storage as its non-volatile
  • Includes magnetic, solid state & optical storage
• What is the difference between Volatile & Non-Volatile?


  Volatile: Volatile storage is temporary meaning data is lost whenever power is turned off. (E.g. RAM)

  Non-Volatile: Non-volatile storage saves even when not being powered. Data can be stored long-term. (E.g. ROM)
• What is primary storage?


  Low capacity, internal storage directly accessed by the CPU

  
  

  Program instructions and data is copied from the hard drive into RAM and are processed by the CPU because primary storage access speeds are much faster than secondary
• What are the two types of primary storage?


  RAM: Volatile and stores all programs that are currently running. Also stores parts of the operating system.

  ROM: Non-volatile and cannot be changed. Stores the BIOS which loads up the operating system
• What is virtual memory?


  An extension of RAM usually known as the HDD (Hard Disk Drive)

  Its beneficial as it allows more programs to be run at the same time with less system slow down.
• What is secondary storage?


  Non-volatile storages used to save and store data. It's not directly embedded on the motherboard causing it to be further away from the CPU so its slower to access than primary
• What are the storage characteristics?

  Capacity: Maximum amount of data that can be stored on the device.

  Durability: How prone it is to breaking

  Portability: How easy it is to carry the device around

  Access speed: How quickly data can be read or edited

  Cost: Price of the storage device

  Reliability: The likelihood of the devices performance over time
• What is binary?


  A base 2 number system consisting of 0's (off) and 1's (on)
• What are the units of data storage?

  4 bits (nibble) is equal to a 8 bits (byte)

  1000 bytes is equal to 1 kilobyte

  1000 kilobytes is equal to 1 megabyte

  1000 megabytes is equal to 1 gigabyte

  1000 gigabytes is equal to 1 terabyte

  1000 terabytes is equal to 1 petabyte
• What is denary?


  A base 10 number system with 10 possible values 0 - 9
• What is hexadecimal?


  A base 16 number system with 16 possible values. Its shorthand for binary as it uses fewer characters making it less prone to errors when reading/writing

  A = 10 B = 11 C = 12 D = 13 E = 14 F = 15
• What is binary addition and its rules?

  Binary addition is the method of adding binary values

  0 + 0 = 0

  1 + 0 or 0 + 1 = 1

  1 + 1 = 0 (carry over 1)

  1 + 1 + 1 = 1 (carry over 1)
• What is an overflow error and when does it happen?

  When a binary value is too large to be stored in the bits available

  With 8 bits, the largest number held is 255 meaning the sum of two binary numbers greater than 255 will result in an overflow error as its too large to be held in 8 bits
• What is binary shift?

  Used to multiply or divide binary numbers

  Shifting to left = multiply Shifting to right = dividing

  
  

  The effect is doubled by each place that is shifted:

  Shifting by 1 = effect of 2

  2 = effect of 4

  3 = effect of 8
• What is a character set?

  A table that matches together a character and a binary value
• What are examples of a character set?

  ASCII:

  • does not take up much memory space
  • uses 8 bit which only gives 256 possible characters
  • enough for the English language

  Unicode:

  • uses 16 bits allowing 65, 536 possible characters
  • different languages can be represented
  • more memory is required to store each character
• How are images made?

  Made of pixels; single-coloured squares arranged on a grid

  Each pixel is assigned a binary value which represents the colour of that pixel
• How do we calculate file size of an image?

  resolution x colour depth
• What is metadata for images?

  Additional data about a file.

  Examples include: height & width in pixels, colour depth, resolution and file type
• How do we convert analogue sound to binary?

  Via digitally recording and storing the analogue sound waves in binary

  To record the sound, the amplitude of the analogue sound wave is measured and recorded in binary at specific intervals
• Why do we sample an analogue sound wave?

  In order to achieve the highest quality sound, many samples are taken to recreate the analogue wave as closely as possible
• What is sample rate?


  The number of times per second the amplitude of the sound wave is measured. It's measured in kilohertz.

  The higher the sample rate, the better the audio quality as digital data closely resembles an analogue wave

  However, higher sample rates result in larger file size as more data is stored
• What is bit depth in sound?

  The number of bits available to represent each sample. A common bit depth is 16 bits

  Higher bit depth, the more bits available therefore quality is often higher as the wave closely resembles an analog wave

  File size will be also be larger, as each sample stores additional bits
• How do we calculate sound file size?

  sample rate x bit depth x duration
• What is lossy compression?

  Where data is permanently removed from file reducing its size

  Uses: images, audio and videos

  Advantages: greatly reduced file size, less bandwith

  Disadvantages: loses data, worse quality
• What is lossless compression?

  Where data is temporarily removed but is then restored to its original state when opened

  Uses: executable files and word documents

  Advantages: no reduction in quality, decompresses files can be reverted to original

  Disadvantages: only slight reduction in size