1.1.1 Architecture of the CPU

What is a computer?

Electronic device that:

• Takes input

• Processes data

• Delivers output

What is the purpose of the CPU?

Fetch, decode, and execute instructions

What happens in the fetch stage?

• Next instruction fetched from main memory

• Stored using registers

What happens in the decode stage?

Instructions are inspected to find out what needs to be done

What happens in the execute stage?

• Going back to main memory — fetching data

• ALU performing calculation

• Storing information in main memory

Describe what happens during the fetch-execute cycle

• Instructions fetched from main memory

• Instructions are decoded

• Instructions are executed

  • ALU performs arithmetic calculations

What components does the CPU consist of?

• ALU — arithmetic logic unit

• CU — control unit

• Cache

• Registers

What is the function of the ALU?

Performs:

• mathematical calculations

• logical operations

• binary shift operations

What is the function of the CU?

• Sends signals to coordinate processor

• Decodes instructions

What is the function of the cache?

Provides fast access to frequently used instructions and data

What are registers?

• Tiny, very fast pieces of onboard memory inside CPU

• Have specific purposes

What does the Von Neumann architecture consist of?

• CU — control unit

• ALU — arithmetic logic unit

• RAM — random access memory

• Inputs and outputs

What concept is the Von Neumann architecture based on?

Stored program concept

Von Neumann Architecture:

Both ____________ _______ and ____________ _______ are stored in the same memory in ________ form.

• instruction data

• program data

• binary

What registers are in a Von Neumann CPU?

• PC — program counter

• MAR — memory address register

• MDR — memory data register

• ACC — accumulator

What is the function of the PC?

• Holds address of next instruction to be executed in memory

• Increments in each FDE cycle

What is the function of the MAR (memory address register)?

Holds memory address where data is to be fetched from or written to

What is the function of the MDR (memory data register)?

Holds data fetched from memory

What is the function of the ACC (accumulator)?

Holds results of calculations performed by ALU

Why is the fetch-execute operation of a CPU described as a cycle?

Once one instruction has been fetched and executed the CPU can fetch and execute the next one