Computer fundamentals 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 processor is redesigned with a larger cache. Which statement best explains why many programs then run faster?

• Data that is used repeatedly sits in faster memory, so main memory is read less often.
• Cache is slower than main memory but larger, so more data can be kept ready.
• The clock speed of the processor rises in proportion to the size of the cache.
• Programs no longer have to be copied from secondary storage into main memory before they run.

Answer: Data that is used repeatedly sits in faster memory, so main memory is read less often.

Cache is small and fast, not large and slow, and the gain comes from locality of reference: the same instructions and values are needed again shortly afterwards.

Which statement describes how instructions and data are held in a machine built on the von Neumann architecture?

• Both share one main memory and are told apart only by how the processor uses them.
• Instructions are kept in ROM and data in RAM at all times.
• Instructions are kept in the control unit and data in the accumulator.
• Instructions are kept in a physically separate memory that the data bus cannot reach.

Answer: Both share one main memory and are told apart only by how the processor uses them.

The stored-program idea is that a single memory holds both, which is why a program can be loaded like any other file. Separate instruction and data memories describe the Harvard design instead.

A laptop loses power while a long report is being typed and the unsaved work disappears. Which property of the memory that held the report explains this?

• It stores data as magnetised regions that decay without power.
• It is read-only, so nothing typed can ever be written back to it.
• It is volatile, so its contents are kept only while power is supplied.
• It is accessed sequentially, so unsaved data can no longer be located after a restart.

Answer: It is volatile, so its contents are kept only while power is supplied.

RAM needs a constant supply to hold its charge, which is why work must be written to secondary storage if it is to survive a power cut.

A processor writes a value into a location in main memory. Which combination of buses carries the location number, the value and the write signal?

• Data bus for the location number, address bus for the value, control bus for the signal.
• Control bus for the location number, address bus for the value, and data bus for the write signal.
• Address bus for the location number, control bus for the value, data bus for the signal.
• Address bus for the location number, data bus for the value, control bus for the signal.

Answer: Address bus for the location number, data bus for the value, control bus for the signal.

The address bus says where, the data bus carries what, and the control bus states whether the operation is a read or a write; mixing these three roles up is a frequent slip.

When a computer is switched on, where is the small start-up routine that begins loading the operating system normally held?

• In cache memory inside the processor
• In read-only memory on the mainboard
• In random access memory
• On the hard disk inside a user data folder

Answer: In read-only memory on the mainboard

RAM is empty at power-on, so the routine has to live in non-volatile memory that the processor can address immediately, and that is firmware held in ROM rather than a file in secondary storage.