Chapter 6 - Storage devices

Question 1

Need for secondary storage

Answer 1

Processor primarily uses RAM and not secondary storage because it is not directly accessible and has slower access speeds, but it retains its contents when the power is off

Question 2

RAM and ROM

Answer 2

• RAM - Stores programs and data currently being used; Volatile (data lost when power is off)
• ROM - Holds information that needs to be permanently in memory e.g. bootstrap loader – program that starts up OS in RAM, which then starts up all other applications); Used in embedded systems e.g. washing machines, cameras because they perform the same tasks

Question 3

Virtual storage

Answer 3

• an extension of RAM, but on the hard disk
• used when RAM fills up and too many programs are running
• OS swaps pages depending on which program is in use, but if this is done too much, performance deteriorates and leads to disk thrashing

Question 4

Storing data

Answer 4

Storage devices use a technique which allows them to create and maintain a toggle state without power to represent either 1/0

Question 5

Hard disk

Answer 5

• ferrous particles on disk are polarised to N/S (= 1/0)
• disk divided into tracks, subdivided into sectors
• disk spins and drive head moves across to access tracks/sectors
• less portable than optical or solid state media
• huge capacity makes them suitable for desktop computers

Question 6

Optical disk

Answer 6

• rewritable (CD-RW): high power laser ‘burns’ disk to make them less reflective, so low power laser shines light and different amounts are reflected back (= 1/0)
• read only (CD-ROM): where pit starts/ends between lands, light is not reflected well (= 1/0)
• Blu-Ray: use of shorter wavelength laser can create smaller pits and wind into tighter spiral
• very cheap to produce and easy to send through the post for distribution purposes
• can be corrupted or damaged easily by excessive sunlight or scratches

Question 7

Solid-state disk

Answer 7

• NAND flash memory cells and a controller
  1. current delivered along bit and word lines to make electrons flow from source to drain
  2. current on word line forces some electrons across insulated oxide layer into floating gate
  3. electrons are trapped once power is off and charge is measured (= 1/0)
• low capacity than hard disks
• one piece of data is accessed just as fast as another due to no moving parts, less susceptible to damage
• consume less power, so stay cooler, ideal for laptops
• silent in operation, lighter and highly portable