1.1.1 Architecture of CPU

Question 1

What is a CPU?

Answer 1

The CPU or Central processing unit is the ‘brains’ of a computer

Question 2

What is the purpose of a CPU?

Answer 2

It’s main purpose is to carry out the FETCH-DECODE-EXECUTE cycle

Fetch information from main memory
Decode instructions - interprets
Executes instructions - performs the instructions

Question 3

What arr the CPU components?

Answer 3

Cache, CU and ALU

Question 4

What is the cache?

Answer 4

Memory that provides fast access to frequently used instructions and data without having to go back to the main memory (RAM)

Question 5

What is the CU (Control Units?)

Answer 5

Decodes instructions and sends signals to control how data moves around CPU

Question 6

What is the ALU ( Arithmetic Logic Unit)?

Answer 6

This is where all arithmetic (add, subtract, multiply, divide) and logical (AND,OR,NOT) operations are carried out

Question 7

What is registers?

Answer 7

A small amount of memory each with their own function - introduced in the Von Nuemann Architecture

Question 8

What are the 4 registers?

Answer 8

MAR,MDR,PC and ACC

Question 9

What is the MAR (Memory Address Register)?

Answer 9

Stores the memory address where data is to be stored or fetched

Question 10

What is the MDR (Memory Data Register)?

Answer 10

Holds data fetched from or to be written to the main memory

Question 11

What is the PC (Program counter)?

Answer 11

Holds the addresses of the next instructions, increments (goes up) by 1

Question 12

What is the ACC (Accumulator)?

Answer 12

Holds the results of calculations from ALU

Question 13

What are examples of input, output and storage?

Answer 13

Input - keyboard, mouse, microphones, web cam, controller
Output - speakers, monitor, headphones
Storage - disc, hard drive, solid state drive (SSD)

Question 14

What does FETCH do?

Answer 14

• The program counter is checked, as it holds the address of the next instruction to be executed
• The Memory Address Register (MAR) uses this address to fetch the required instruction from main memory (RAM) and bring it into the CPU
• The address in the program counter is incremented (its value is increased by one) to point at the next instruction

Question 15

What does DECODE do?

Answer 15

• Now the instruction is in the CPU, the Control Unite (CU) decodes it - i.e, the CU works out what needs to be done

Question 16

What does EXECUTE do?

Answer 16

• What happens during the execute stage depends on the instruction - the CPU may:
• Fetch data from memory to be used in a calculation
• Jump to another instruction that is out of sequence
• Write data held in the accumulator back into main memory (RAM)