1.1.3 Input, output and storage

Question 1

Factors to consider when choosing secondary storage

Answer 1

• Capacity
• Speed
• Cost
• Portability
• Reliability
• Durability
• Size

Question 2

How does magnetic storage operate?

Answer 2

• Disk unit usually comprises of one or more double-sided metal platters with a magnetic coating.
• Data is represented on the surface of the platters with tiny magnetised dots.
• To read data, the head has a small magnetometer that sweeps along the tracks and reads the states.
• To write data, the magnet on the end of the read/write head is used to generate a small magnetic field, causing dots to switch states.

Question 3

Characteristics of magnetic storage

Answer 3

• Low cost.
• High capacity.
• Poor durability - many moving parts.
• Relatively low speed.
• Medium Portability.
• Not very compact.

Question 4

Characteristics of optical storage

Answer 4

• Low cost.
• Medium capacity - up to 100GP for Blu-ray.
• Poor durability - prone to scratches.
• Relatively low speed.
• Low cost.
• Very portable.
• Low reliability.

Question 5

How does optical storage operate?

Answer 5

• Binary is represented via pits and lands on the surface of the disk.
• 3 different types: ROM, R- and RW-
• To read, a laser is reflected off of the pits and lands to determine the state.
• To write to R- or RW-, a higher intensity laser is used to burn the pits and lands into the disk.
• RW- can have data removed with chemicals.
• ROM cannot be written to after manufacturing.

Question 6

How does solid state operate?

Answer 6

• Comprised of millions of NAND flash cells.
• Each cell has a floating gate transistor that can trap electrical charge to represent binary.

Question 7

Characteristics of solid state storage?

Answer 7

• Very high speed.
• High capacity.
• High cost.
• High portability.
• High durability - no moving parts.
• Medium reliability - limited number of read/write cycles.

Question 8

What is cloud storage?

Answer 8

• Data stored on an external server with secondary storage devices that are owned by commercial organisations.
• Transferred over the internet.

Question 9

Advantages of cloud storage

Answer 9

• Can access anywhere with an internet connection.
• Expandable storage.
• Safe way to back up files as the provider takes vulnerability.
• Makes sharing files easier.

Question 10

Disadvantages of cloud storage

Answer 10

• Requires a relatively fast internet connection.
• Can take a long time to access/download large files.
• Could be a security risk as large cloud storage providers are targets of malicious attacks.

Question 11

Differences between RAM and ROM

Answer 11

• RAM is volatile whereas ROM is non-volatile.
• RAM has a larger capacity than ROM.
• RAM stores data that is currently being used whereas ROM stores boot up instructions.
• RAM is read/write whereas ROM is read only.

Question 12

What is virtual memory and how does it work?

Answer 12

• Section of secondary storage used as RAM when too many applications are open for the physical RAM to handle.
• When virtual memory is required, the OS creates a set of virtual addresses.
• Data moved to virtual memory is stored in pages.
• When the CPU is ready to use data in virtual memory, it must be moved to the RAM first.