2.1.2

Question 1

Inputs

Answer 1

• An input is any data required to solve the
  problem.
• These may be entered by the user, or
  obtained from hardware such as a sensor.

Question 2

Outputs

Answer 2

• Outputs are the solutions to the problem
  which are returned.
• They can only be produced once the
  input has been processed.
• It is important to consider the methods
  used to capture data from the user and to
  present it back to them.
• Think about the data structures used.
• Think about the devices used.
• Think about what outputs are needed
  first.

-Use this information to consider what
inputs are needed to produce the
required output.

Question 3

Preconditions

Answer 3

• Things which are needed before the program can run.
• The code expects the information passed to it to meet certain criteria.
• The code may test for these when it is run.
• They may instead be included within
  documentation.
• Including this information within documentation reduces the complexity of
  the program and makes it easier to use.
• Preconditions make it easier to reuse subroutines.

Question 4

Caching

Answer 4

• Values or information can be stored in memory after use.
• Prefetching uses an algorithm to predict which instructions may be needed next and store them in cache before they are needed.
• The accuracy of the algorithm’s predictions influences the effectiveness of this technique.

Question 5

Caching advantages

Answer 5

• Values or information can be stored in memory after use.
• This makes it quicker to retrieve them if they are needed again.
• Web pages are also cached in this way to improve load times and reduce bandwidth usage.
• Prefetching uses an algorithm to predict which instructions may be needed next and store them in cache before they are needed.
• This reduces the need to wait for an instruction to be loaded.

Question 6

Caching drawbacks

Answer 6

• A large cache can take a long time to search.
• Caching and prefetching can be difficult to implement.

Question 7

Reusable Program Components

Answer 7

• Common functions can be packaged into a library.
• This makes it easier to reuse them throughout a project.
• Abstract data structures, subroutines
  and classes can all be reused in this
  way.
• Decomposition is used to indicate
  where components of an existing program can be reused.
• Reusable components have already been tested and so are more reliable.
• They make development less time consuming and therefore less costly.