1.3 Secondary storage 1: optical and magnetic devices

Question 1

three main types of storage devices

Answer 1

magnetic discs - data is stored using magnetism

optical disks - data is stored using ‘pit and lands’

solid state (flash) memory - data is stored using semiconductor chips

Question 2

need for secondary storage

Answer 2

ROM can’t be used to save files as it is read only

RAM can’t be used to save files as it is volatile

programs and data need to be saved on a type of storage that is read/write and non-volatile

Question 3

primary storage

Answer 3

RAM, ROM, registers and cache

Question 4

secondary storage

Answer 4

where the OS, programs and data are held when not in use

Question 5

tertiary storage

Answer 5

backups and archives of large amounts of data

Question 6

magnetic storage

Answer 6

used in hard disk drives (HDDs) and digital tape drives

consist of stacks of non-removable discs coated with magnetic materials

data is encoded as opposing magnetic polarities on the surface of the disc

electromagnets in the read/write heads read and write the data

Question 7

common use for digital tape drives

Answer 7

backing up large computer systems

Question 8

cost of magnetic storage

Answer 8

very low

hard drive discs in budget laptops have capacities of at least 1 terabyte

Question 9

optical storage

Answer 9

includes:

• compact discs (CDs) that store 700MB
• digital versatile discs (DVDs) that store 4.7 GB
• blu-ray discs that store up to 50GB

optical discs use a laser to read and write data

the data is encoded as a series of pits in a spiral track running from the inside to the outside of a disc

Question 10

A small business backs up the data on its computer system every day.

Compare backing up the data to a magnetic hard disc with backing up to an optical disc [4]

Answer 10

data is written to and read from a magnetic hard disc more quickly than to/from an optical disc, so backing up and restoring would be quicker

hard discs are permanently located within a hard disc drive so are less portable than optical discs, such as DVDs, which can be removed from the drive when not in use

portable hard drives are very light and compact so could be stored off-site

optical media tends to be more durable than magnetic media
DVDs offer unlimited storage because the business can use as many as needed

HDDs can store several terabytes of data which would probably be enough for the business

Question 11

Explain why secondary storage devices are needed [3]

Answer 11

unlike RAM that is volatile, secondary storage doesn’t lose its contents when there is no power

this means that it can provide permanent storage for programs and data that would otherwise be lost when the computer is switched off