1.1.2 Von Neumann Architecture

Question 1

ALU

Answer 1

• The ALU performs all of the arithmetic and logical operations of the CPU, including:
  . Addition and subtraction, multiplication and division.
  . Comparisons such as whether numbers are equal or if one is greater than another.
  . Boolean operations (e.g. AND, OR, NOT).

Question 2

CU

Answer 2

• The Control Unit transmits control signals to other components of the CPU.
• The Control Unit follows the fetch-decode-execute cycle to execute program instructions

Question 3

Components of the CU

Answer 3

• The clock, which coordinates the CPU’s activity.
• The decoder, which decodes program instructions.

Question 4

Registers

Answer 4

• The Control Unit transmits control signals to other components of the CPU.
  They are used to hold information needed for the CPU to work.
  Each register holds a specific piece of information.

Question 5

PC

Answer 5

The PC holds the memory location address of the next instruction to be performed by the CPU

Question 6

MAR

Answer 6

The MAR holds the address of the location in memory where data is to be retrieved or stored.

Question 7

ACC

Answer 7

The ACC holds the result of calculations and operations performed by the arithmetic logic unit

Question 8

MDR

Answer 8

The MDR holds the data that has been retrieved from memory, or that is about to be stored in memory

Question 9

Fetch, Decode, Execute

Answer 9

To process instructions and data, the processor needs to retrieve them from memory. To do this, it follows the fetch, decode, execute (FDE) cycle

Question 10

Fetch

Answer 10

• The address of the instruction that needs to be processed next is copied from the Program Counter (PC) to the Memory Address Register (MAR).
• The PC is incremented to point to the next instruction that will be needed when the cycle starts again.
• The instruction stored at the location held by the MAR is copied to the MDR.

Question 11

Decode

Answer 11

The Control Unit decodes the instruction and sends control signals to the component within or outside the CPU that needs to act.

Question 12

Execute

Answer 12

The operation indicated by the instruction is performed by the appropriate component. For example
The Arithmetic Logic Unit (ALU) performs the operation given by the Control Unit.
The value stored by the Program Counter or Memory Address Register might be changed.

Question 13

What happens during the Fetch, Decode, Execute cycle

Answer 13

. The address of the next instruction is copied from thePC to the MAR

. ThePC is incremented to point to the next instruction

. The instruction stored at the location held by the MAR is copied to the MDR