IB Computer Science practice questions.

A processor is about to read an instruction from main memory. Which register holds the location number that is placed on the address bus?

• The memory data register (MDR)
• The memory address register (MAR)
• The accumulator (ACC)
• The current instruction register (CIR)

Answer: The memory address register (MAR)

The MAR receives the address, which travels along the address bus, and whatever comes back arrives in the MDR. Swapping these two registers is the commonest slip in machine instruction cycle questions.

A college owns every cable and switch that joins the three buildings standing on its single campus. How should this network be classified?

• A WAN, because three separate buildings have to be linked together
• A MAN, because the network reaches beyond a single street address
• A LAN, because it is one site with self-owned links
• A PAN, because a single organisation controls every device

Answer: A LAN, because it is one site with self-owned links

A LAN is defined by a single site and by the organisation owning the connecting infrastructure, not by how many buildings or machines are involved. A WAN begins where the links have to be leased from a carrier that crosses public land.

A sports club replaces its collection of separate spreadsheet files with a relational database run by a database management system. Which task is now handled by the DBMS instead of by each application program?

• Controlling how records are stored on disk
• Deciding which discount a returning family receives
• Choosing the layout of the printed membership report
• Wording the error message shown to the clerk on screen

Answer: Controlling how records are stored on disk

The DBMS takes over storage, indexing and controlled access to the data, which is what gives every application one consistent view of it. Business rules such as discounts, and the presentation of reports or messages, stay in the application.

A postal company wants software that reads handwritten postcodes. Rather than a programmer stating a rule for every possible shape, the company supplies thousands of scanned postcodes together with the characters they contain. Which statement best describes why this is a machine learning approach?

• The rules separating one character from another are derived from the supplied examples.
• The program stores every supplied image and returns the one that is asked for.
• A programmer states every rule in advance and the software applies them in order.
• The software is translated into machine code before it is executed on the sorting machine.

Answer: The rules separating one character from another are derived from the supplied examples.

Machine learning is defined by where the rules come from: the model infers them from data instead of receiving them from a programmer. Storing and retrieving the examples unchanged would be a lookup, not learning.

A design team splits a hospital appointment system into a booking part, a reminder part and a billing part, and writes a separate specification for each. Which approach to computational thinking are they applying?

• Decomposition
• Abstraction
• Pattern recognition
• Algorithm evaluation

Answer: Decomposition

Breaking a system into parts that can each be specified, built and tested on their own is decomposition. Abstraction would mean discarding detail from the situation, not creating separate parts of the solution.

A booking system must store a customer telephone number that begins with a zero and is never used in a calculation. Which data type is the most suitable?

• Integer
• Real
• String
• Boolean

Answer: String

Stored as a number the leading zero would be lost and no arithmetic is ever wanted on the value, so the digits are held as characters. A telephone number looks numeric but behaves like text.