← IGCSE Computer Science Paper 1

Von Neumann architecture

A computer design where instructions and data share the same main memory (RAM) and the CPU fetches them one at a time. This is the stored program concept, named after John von Neumann.

Part of: IGCSE Computer Science 0478 — 3.1 Computer Architecture — Module 5

Understanding Von Neumann architecture in IGCSE Computer Science Paper 1

What it does: The RAM contents show instructions (LDA, ADD, STO) and data values (5, 7) stored side by side in one memory. The CPU and RAM are separate components, and instructions travel from RAM to the CPU one at a time, as Von Neumann architecture describes. The design is named after the mathematician John von Neumann, who described the stored program idea. The CPU fetches one instruction at a time, then decodes and executes it before fetching the next. The CPU processes instructions and RAM stores them. They are separate parts linked by buses. The ALU and control unit are inside the CPU. Registers such as the PC, MAR, MDR, CIR and ACC are also part of the model. A monitor and keyboard are input and output devices, not parts of the architecture.

Common mistakes: Von Neumann architecture uses one shared main memory for both instructions and data. Separate memories belong to a different design. It should be memory = "one shared RAM". In Von Neumann architecture the instructions and data share the same memory, so shared should be True.

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Learning
Duo
In Von Neumann architecture, where are program instructions stored?
In a separate memory used only for instructionsIn main memory (RAM), along with the data
Matches
Von Neumann: instructions are stored in one memory and data in a separate memory
↓
Von Neumann architecture uses one shared main memory for both instructions and data, not two separate memories.
Applying
Meanings
Term
Von Neumann architecture
Meaning
A computer design where instructions and data share the same main memory (RAM) and the CPU fetches them one at a time. This is the stored program concept, named after John von Neumann.
Practice
// Von Neumann architecture
Testing
Gaps
Instructions and data share the same
Check Answer
Spots
1memory = "two separate RAMs"
2holds = "instructions + data"

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Quick Questions

1. In Von Neumann architecture, where are program instructions stored?
A. In a separate memory used only for instructions
B. In main memory (RAM), along with the data ✓
Von Neumann architecture uses one shared main memory for both instructions and data. This is the stored program concept.
2. Which statement about Von Neumann architecture is true?
A. Instructions and data share the same memory ✓
B. Instructions and data each have their own memory
Sharing one memory is the key feature. A design with separate memories for instructions and data is not Von Neumann.
3. Who is Von Neumann architecture named after?
A. John von Neumann ✓
B. Alan Turing
The design is named after the mathematician John von Neumann, who described the stored program idea.
4. How does the CPU get instructions in Von Neumann architecture?
A. It fetches every instruction at once
B. It fetches them from RAM one at a time ✓
The CPU fetches one instruction at a time, then decodes and executes it before fetching the next.
5. The stored program concept means that...
A. the program is held in memory so the CPU can fetch it ✓
B. the program is built into the CPU and cannot change
In the stored program concept, instructions are kept in main memory, just like data, and the CPU fetches them from there.

Match the Pairs

Von Neumann architecture → A computer design where program instructions and data share the same main memory and the CPU fetches them one at a time
Stored program concept → Program instructions are held in main memory (RAM) alongside data, so the CPU can fetch them one by one to run the program
Instructions and data are held together in the same main memory → RAM: [LDA 20] [ADD 21] [STO 22] [5] [7] [ ]
The CPU and RAM are separate parts, and the CPU fetches one instruction at a time from RAM → CPU <-- fetch one instruction at a time <-- RAM
Von Neumann: instructions are stored in one memory and data in a separate memory → Von Neumann architecture uses one shared main memory for both instructions and data, not two separate memories.
Von Neumann: the CPU fetches all instructions from RAM at the same time → The CPU fetches instructions one at a time, not all at once.

Key Term

Von Neumann architecture
A computer design where instructions and data share the same main memory (RAM) and the CPU fetches them one at a time. This is the stored program concept, named after John von Neumann.

Fill in the Blanks

1. Instructions and data share the same memory
Hint: Type the word for the single place where both instructions and data are kept.
2. The CPU fetches instructions one at a time
Hint: Type the number word for how many instructions the CPU fetches at once.
3. Named after John von Neumann
Hint: Type the surname of the scientist this architecture is named after, including the 'von' part.
4. The CPU and RAM are separate components
Hint: Type the abbreviation for the processor, which is a separate part from main memory.
5. The stored program concept uses RAM
Hint: Type the two-word name for the idea that programs are kept in memory along with data.

Spot the Error

Question 1
A memory = "two separate RAMs"
B holds = "instructions + data"
C cpu_fetch = "one at a time"
Line A — Von Neumann architecture uses one shared main memory for both instructions and data. Separate memories belong to a different design. It should be memory = "one shared RAM".
Question 2
A cpu = "processor"
B ram = "main memory"
C shared = False
Line C — In Von Neumann architecture the instructions and data share the same memory, so shared should be True.
Question 3
A program = "stored in RAM"
B data = "stored in RAM"
C fetch_per_cycle = "all"
Line C — The CPU fetches items from memory one at a time, not all at once. It should be fetch_per_cycle = 1.
Question 4
A parts = ["CPU", "RAM"]
B cpu_role = "store programs"
C ram_role = "store programs, data"
Line B — The CPU fetches and executes instructions. It is RAM that stores the programs and data. It should be cpu_role = "fetch and execute".
Question 5
A ram = {}
B ram[0] = "LOAD 7"
C ram[1] = 25
D fetched = ram[0], ram[1]
Line D — The CPU fetches one item at a time from memory. It cannot fetch two in one step. It should be fetched = ram[0].

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