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Leaving Cert Computer Science: CPU, memory & storage

How often CPU, memory & storage comes up on the Computer Science papers, every year it was asked, and questions to try.

HL Asked on 5 of the last 5 Higher Level papers, most recently in 2025. banker

OL Asked on 4 of the last 5 Ordinary Level papers, most recently in 2025. most years

CPU, memory & storage, Higher Level(6 marks)

Quick ones on CPU, memory & storage.

(a)Which CPU register holds the address of the next instruction to fetch?
  1. Accumulator
  2. Program counter
  3. Memory data register
(b)Which part of the CPU carries out calculations and comparisons?
  1. The cache
  2. The control unit
  3. The ALU
(c)In what order does a CPU process each instruction?
  1. Fetch, decode, execute
  2. Execute, fetch, decode
  3. Decode, fetch, execute
Show the answers

(a) Program counter

(b) The ALU

(c) Fetch, decode, execute

Your turn: Higher Level questions on CPU, memory & storage.

Higher Level

Asked on 5 of the last 5 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025A12
2024A8
2023B14
2022A2
2021A3

Links open the State Examinations Commission’s paper for that year.

More CPU, memory & storage questions

CPU, memory & storage, 2 marks

What is a CPU's clock speed measured in?

  1. Bytes, e.g. gigabytes (GB)
  2. Bits per pixel
  3. Hertz, e.g. gigahertz (GHz)
Show the answer

Hertz, e.g. gigahertz (GHz)

Clock speed is cycles per second: 3 GHz means about 3 billion cycles each second. Gigabytes measure storage, not speed.

CPU, memory & storage, 3 marks

What is one advantage of a quad-core CPU over a single-core CPU of the same clock speed?

  1. It needs no RAM, as each core has its own
  2. Several tasks can be processed at the same time
  3. It stays cool under load, so it needs no fan
Show the answer

Several tasks can be processed at the same time

Each core runs its own instructions, so several programs, or one program that splits its work, run faster. Not every task can be split this way.

CPU, memory & storage, 2 marks

Which CPU register holds the results of calculations done by the ALU?

  1. The accumulator
  2. The program counter
  3. The control unit
Show the answer

The accumulator

The accumulator stores the ALU's latest result. The program counter holds the address of the next instruction, and the control unit is not a register.

Ordinary Level

Asked on 4 of the last 5 Ordinary Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025A2, A8
2024Not asked
2023A7
2022A4, B13
2021B15

Links open the State Examinations Commission’s paper for that year.

More CPU, memory & storage questions

CPU, memory & storage, 2 marks

Which part of the CPU does the arithmetic and makes comparisons?

  1. Control unit
  2. Cache
  3. ALU
Show the answer

ALU

The Arithmetic Logic Unit adds, subtracts and compares values (e.g. is x > 5?). The control unit directs the other parts.

CPU, memory & storage, 2 marks

Which part of the CPU decodes instructions and controls the other parts?

  1. Main memory (RAM)
  2. Control unit
  3. Arithmetic unit (ALU)
Show the answer

Control unit

The control unit manages the fetch-decode-execute cycle and sends signals telling the ALU, memory and devices what to do.

CPU, memory & storage, 2 marks

The three stages of the CPU's main cycle are fetch, decode and…

  1. Execute
  2. Save
  3. Compile
Show the answer

Execute

The CPU fetches an instruction from memory, decodes what it means, then executes it, billions of times a second.

Other Computer Science topics

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