[1.1.1] | 1: Inside a CPU

Question 1

What is the CPU?

Answer 1

• The hardware component responsible for executing program instructions.
• It does this through the FDE cycle.

Question 2

What does Moore’s Law state?

Answer 2

• The number of transistors that can fit on a given space would double every 2 years.
• We are reaching the physical limitations of this theory and it is now more like 3 years.

Question 3

What is the Control Unit’s function?

Answer 3

• To organise the flow of data between CPU components (by sending out control signals).
• It performs the FDE cycle and contains the clock, which determines its speed.

Question 4

What is the Arithmetic Logic Unit’s function?

Answer 4

• It carries out arithmetic, logical and comparative calculations.

Question 5

What is a register’s function and what are the two types of registers?

Answer 5

• A discrete, high speed memory location that holds one piece of data.

• General Purpose: Can be used to store the immediate results of calculations.
• Special Purpose: Designed to fulfill a specific role.

Question 6

List 2 Registers that store locations and give their functions.

Answer 6

• PC: Holds the location of the next instruction.
It is incremented after each FDE cycle to always point to the next instruction.
(It can encounter a jump instruction which means it would not increment.)

• MAR: Stores the location of the data to be fetched from / sent to memory.

Question 7

List 3 Registers that store data and give their functions.

Answer 7

• MDR: Stores data fetched from / to be stored in memory.

• CIR: Holds the current instruction.

• ACC: Holds the results of operations performed by the ALU.

Question 8

What does a bus do?
List the 3 main buses in the CPU.

Answer 8

• Buses are communication channels that allow the transport of data around a computer system.

• Address: Provides an address to memory.

• Data: Transfers data between the CPU and memory.

• Control: Provides signals to memory that trigger read / write operations.