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Bus Efficiency 0 / 20
Register Rank Address Scout
1 [2 Marks]
Von Neumann architecture includes registers. Identify two registers used in Von Neumann architecture.
💡 Hint: Think of the abbreviations (e.g. PC, MAR).
✅ Mark Scheme

Any two from:

  • Program Counter (PC)
  • Memory Address Register (MAR)
  • Memory Data Register (MDR)
  • Accumulator (ACC)
  • Current Instruction Register (CIR)
⚠️ Examiner's Trap Do NOT list "Cache" or "ALU". These are components, not registers!
How many did you get right?
2 [4 Marks]
Complete the table by dragging the correct Register Name to its definition.
PC
ACC
MAR
MDR
Register Definition
Stores address of the next instruction. Increments each cycle.
Stores the result of mathematical calculations.
Stores the address of where data is to be fetched/stored.
Stores the data/instruction just fetched from memory.
✅ Mark Scheme
  1. PC (Program Counter)
  2. ACC (Accumulator)
  3. MAR (Memory Address Register)
  4. MDR (Memory Data Register)
Score yourself (1 mark per correct row):
3 [2 Marks]
Describe the purpose of the Program Counter (PC).
💡 Hint: It deals with the 'next' instruction. Does it stay the same?
✅ Mark Scheme
  • Stores the address of the next instruction to be fetched. (1)
  • Increments to point to the next instruction. (1)
⚠️ Misconception Alert Do NOT say "counts the instructions". It stores an address.
Score:
4 [2 Marks]
Describe the purpose of the Accumulator (ACC).
✅ Mark Scheme
  • Stores the result of calculations / arithmetic operations. (1)
  • Stores the result from the ALU. (1)
⚠️ Examiner's Trap Don't say "It does the maths". The ALU does the maths; the ACC stores the result.
Score:
5 [4 Marks]
Explain the difference between the data stored in the MAR and the data stored in the MDR.
💡 Hint: A = Address, D = Data. Where does the data come from?
✅ Mark Scheme
  • The MAR stores the address / location of the data. (1)
  • The MDR stores the data / instruction itself. (1)
  • The MAR holds the address fetched from the PC. (1)
  • The MDR holds the data fetched from Memory/RAM. (1)
Score yourself (Max 4):
6 [6 Marks]
Describe what happens during the fetch-execute cycle. You must refer to the registers in your answer.
💡 Hint: Start at the PC. How do the MAR and MDR hold the address and instruction? What does the CU do?
✅ Mark Scheme Breakdown

Interactive Checklist: Click the points you included to calculate your score.

1. PC holds address of next instruction.
2. MAR holds address of instruction/data to be fetched.
3. MDR holds instruction/data fetched from memory.
4. PC is incremented.
5. Instruction decoded by CU.
6. Result stored in Accumulator (ACC).
Final Score (Based on checks):