Year 11 CPU architecture Revision 1

• Computing
• Upper Secondary (Key Stage 4)
• Lower Secondary (Key Stage 3)

Year 11 System architecture revision

Do Now: State 2 examples of registers.
Extension: What is stored in Ram?

Learning objective 

Strengthening - Recall key CPU concepts and features.

Excelling - Complete exam level answers. 

The CPU

The processor controls all the processing of the computer.

Interprets and executes instructions. 

How does it do this?

• FETCH – causes the next instruction and any data involved to be fetched from main memory (RAM)

• DECODE – decodes the instruction
  

• EXECUTE – the instruction is executed
  

What is the purpose of the CPU?

1. Interpret and execute instructions
2. Store data
3. Download files
4. Store the OS

CPU stands for?

1. Control processing unit
2. Control passing unit
3. Central passing unit
4. Central processing unit

FDE?

1. Fetch decide enhance
2. Find decode enhance
3. Fetch decode execute
4. Fetch decide execute

Stored program concept

Von Neumann architecture is the design upon which many

computers are based.

• Data and instructions are both stored as binary digits
• Data and instructions are both stored in primary memory
• Instructions are fetched from memory one at a time and in order (serially)

Von Neumann architecture uses the ‘stored program’ concept.
What does this mean?

What is stored inside RAM?

Von Neumann architecture

A processor based on Von Neumann architecture has five special registers which it uses for processing:

Register

Not Register

RAM

Rom

MAR

Cache

MDR

ALU

PC

GPU

Control Unit

Why do you think RAM is erased?

Registers

Register are a superfast but small amount of memory inside the CPU

• PC - Stores the address of the next instruction.
• MAR - Stores the address of the current instruction to be fetched
• MDR - Stores the data fetched by the MAR
• ALU -  Completes mathematical and logical problems
• Control unit  - It issues control signals that control hardware, Decodes
• Accumulator - The ACC stores the result of mathematical or logical calculations.

Name and explain the purpose of 3 registers.

Cache memory

Cache memory is temporary storage for frequently accessed data.

 

Cache memory is closer to the CPU than RAM, meaning that it can provide data and instructions to the CPU at a faster rate.

Memory type	Speed	Storage Capacity
Registers
Cache
RAM

Fast

Fastest

Small

Smallest

Large

Very Fast

Which of the following is NOT a function performed by the ALU?

1. Fetching instructions from memory
2. Adding two binary numbers together
3. Performing logical AND operations
4. Comparing if one number is greater than another

Used for temporarily storing arithmetic and logic results. 

Sort the Registers into the correct sequence order.

Points to the next instruction that needs to be executed. It is located in the Control Unit 

Used for holding the address of the

current instruction to be executed,

and the address of data to be used in instruction 

Used for holding the actual instruction or data that is stored in RAM. 

MAR

MDR

ACC

PC

Exam Question (4 marks)

Model answer: 

Model answer (4 marks):

• The Program Counter (PC) sends the address of the next instruction to the Memory Address Register (MAR).
• The instruction at that address is fetched from main memory and loaded into the Memory Data Register (MDR).
• The instruction is transferred from the MDR to the Current Instruction Register (CIR) and decoded.

The Control Unit executes the instruction, which may involve loading/storing data, performing ALU operations, or updating the PC.

Exam Question (4 marks)

Performs mathematical operations

Sends signals to direct operations

Keeps the clock in sync

A small piece of fast memory inside the processor 

A small piece of memory inside the processor the stores frequently used data

Exam question (3 marks)

Model answer 

Model answer (3 marks):

• RAM stores the programs and data that Dipesh is currently using, such as apps and the operating system.
• The CPU fetches instructions and data from RAM, because it cannot work directly from secondary storage.
• The CPU processes these instructions and sends results back to RAM, allowing the tablet to run applications smoothly.