IGCSE · Practice questions · The CPU and Von Neumann architecture

Name the part.

Six original Cambridge-style questions on the CPU, its registers and its buses, with mark-scheme style solutions.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Where and what.

Addresses: PC (next instruction) and MAR (location being accessed now).
Contents: MDR (data or instruction moving to or from memory), CIR (current instruction), ACC (result).
Units: CU decodes and controls; ALU does arithmetic and logic.
Buses: address (one way), data and control (two way).

Recall

[2 marks]

State the role of the central processing unit (CPU) in a computer.

It processes instructions and data that are input into the computer. ✓
So that the result can be output (by fetching, decoding and executing instructions). ✓

Recall

[4 marks]

Name the register described in each case.

(a) Holds the address of the next instruction.
(b) Holds the result of a calculation.
(c) Holds the address of the location about to be accessed.
(d) Holds the instruction being decoded.

(a) Program counter (PC). ✓
(b) Accumulator (ACC). ✓
(c) Memory address register (MAR). ✓
(d) Current instruction register (CIR). ✓

Explain

[2 marks]

Explain what is meant by a Von Neumann architecture.

Instructions and data are stored together in the same memory. ✓
They are fetched by the CPU along the same buses, one after another. ✓

Recall

[3 marks]

Identify the three buses in a Von Neumann computer and state what each one carries.

Address bus: carries memory addresses (from the CPU to memory). ✓
Data bus: carries data and instructions (both ways). ✓
Control bus: carries control signals such as read, write and the clock. ✓

Explain

[2 marks]

Describe the purpose of the arithmetic logic unit (ALU).

It carries out arithmetic calculations, such as addition and subtraction. ✓
It carries out logic operations, such as AND, OR and comparisons. ✓

Analysis

[2 marks]

A student writes: "The MAR stores the data that is read from memory." Explain the mistake.

The MAR stores the address of the memory location, not the data. ✓
The data read from memory is stored in the MDR. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.