Memory and Storage

Memory and Storage

1. Memory

   • Primary Storage
     • Memory that the CPU can read/write to quickly
   • Volatile = power is required for this component to retain data
   • Non-Volatile
     • The components retains data even when the power is turned off
   • RAM = Random access memory
     • The main temporary memory in a computer
     • Volatile
     • Read/Write
     • Programs care copied from Secondary storage to RAM when they are in use
     • Slower than cache but faster than secondary storage
   • ROM
     • The main permanent memory in a computer
     • Non-volatile
     • Only read not write
     • Contains BIOS
       • Instructions needed to boot up the computer

2. Secondary Storage

   • Magnetic
     • 0s and 1s are North and South
     • Hard Disk Drives
       • Moving Parts
         • Can be damaged by impacts or magnetic fields
       • Long Read/Write Life
     • Magnetic Tapes
       • Used by organisations to store huge amounts of data
       • Easily damaged by impacts heat and magnets
   • Optical
     • CDs
     • DVDs
       • Low Speed and capacity
         • Used to store music or films
       • Cheap
   • Solid State
     • No moving parts
       • Shock and Impacts resistant
     • SSDs
     • Flash Drives and Memory Sticks
       • Used to expand the capacity of small devices or to physically move data

3. Virtual Memory

   • If RAM is full some data is moved to a part of secondary storage
   • The data is moved back to RAM when the CPU needs it.
   • Data transfer is slower on secondary storage
     • Computer Slows down

4. Compression

   • Lossy
     • Store a lower number of colours
     • Store bigger areas of pixels s 1 colour
     • Reduces quality of the image or video
       • Mostly not noticible
       • ood compromise of quality and file size and download time
     • Only for pictures sound and video
   • Lossless
     • Instead of storing every pixel we store the colour and the amount of pixels in that row with that collour
     • Only suitable for cartoons and clip art
     • MUST be used for text documents and executable programs
     • Less effective at reducing the file size
   • Reduces file size so it takes up less space
     • Maximise the amount you can store
     • Quick internet transfer

5. Character Sets

   • Collection of characters that a computer recognises from their binary representation
   • ASCII
     • Each character is given a 7-bit binary code
     • Only has english and numbers and some characters
   • Unicode
     • Each character is 16 bits
     • 65536 Characters
     • First 128 charcters are the same for both

6. Storing Images and Sound

   • Images
     • BITMAP
       • a type of image made up of pixels
         • Each pixel colour has a binary code
     • Image resolution
       • Width x Height
     • Colour Depth
       • Number of bits for each colour
     • File Size = image resolution x colour depth
     • METADATA
       • data stored with a file containing information about the file
         • Height and Width
         • Colour Depth
         • Resolution
         • Author and date created
   • Sound
     • Sampling
       • Converting an analogue sound wave into a digital data that can be stored and read by a computer
     • Sample Rate
       • Number of samples taken per second
     • Bit Depth
       • Number of bits for each sample