1.2 Memory & Storage

What you should know

1.2.1 Primary Storage

• The need for primary storage

primary storage includes: RAM, ROM and Cache

• difference between RAM and ROM

RAM - Random Access Memory 

• • • Volatile - contents are lost when power is switched off

    • Fairly large - 1, 2, 4 or 8 Gigabytes (a gigabyte is 1,000 megabytes)

ROM  - Read Only Memory

• • • Non-Volatile - contents are retained when power is lost

    • quite small - 2 or 4 MegaBytes

• purpose of ROM in a computer system

• • • • stores the instructions required to get the computer started (the boot process)  

• purpose of RAM in a computer system

• • • • Main memory

      • holds data and programs currently in use

      • stored programs are loaded from Hard drive to RAM, then processed by CPU

• the need for virtual memory

• • • • needed when there is not enough RAM 

      • uses a section of the hard drive as a temporary store

      • much slower than RAM 

1.2.2 Secondary Storage

• the need for secondary storage

• • Primary storage is RAM which is volatile - disappears when power is switched off

  • secondary storage is non-volatile - information and programs are retained even when power is lost

  • secondary storage is generally much bigger than RAM 

• data capacity and calculation of data capacity requirements

• • text files tend to be smaller than images, sound and video files

• common types of storage:

⃝ optical - ie DVD or CD

⃝ magnetic - Hard Drives, Floppy discs, Tape drives

⃝ solid state - SSDs, SD Cards, USB Sticks

• suitable storage devices and storage media for a given application

the advantages and disadvantages of each type will depend on their characteristics:

⃝ capacity  - magnetic holds most

⃝ speed - Solid state is fastest

⃝ portability - Solid state is most portable

⃝ durability - Magnetic is most durable

⃝ reliability - Magnetic or Solid State is most reliable 

⃝ cost - Magnetic is cheapest per MB