Von Neumann Architecture (Cambridge (CIE) O Level Computer Science)

Von Neumann Architecture

What is the Von Neumann architecture?

• The Von Neumann Architecture is a design of the CPU which was proposed by Mathematician John Von Neumann in the 1940s, which most general-purpose computers are built upon

• The Von Neumann Architecture outlines how the computer memory, input/output devices and processor all work together 

• The Von Neumann architecture consists of:

  • Control unit (CU)

  • Arithmetic logic unit (ALU)

  • Registers

  • Buses

What is the function of each component?

Arithmetic logic unit (ALU)

• Performs arithmetic operations

• Performs logical decisions

  • IF X > 5 THEN
          DO ……….

Control unit (CU)

• Coordinates how data moves around the CPU by sending a signal to control the movement of the data 

• Decodes the instructions fetched from memory

Registers

• Extremely small, extremely fast memory located in the CPU

• Hold small amounts of data needed as part of the fetch-execute cycle

• Each register has its own specific purpose

• It consists of 5 main registers

  • The Program Counter (PC)

  • The Memory Address Register (MAR)

  • The Memory Data Register (MDR)

  • The Accumulator (ACC)

  • Current Instruction Register (CIR)

• For each of the registers you must know 

  • The name of the register

  • Its acronym

  • The purpose of the register

Buses 

• Components within the CPU and wider computer system are connected by buses

• A bus is a set of parallel wires through which data/signals are transmitted from one component to another

• There are 3 types of bus:

  • Address - unidirectional, carries location data (addresses), data is written to/read from

  • Data - bidirectional, carries data or instructions

  • Control - bidirectional, carries commands and control signals to tell components when they should be receiving reads or writes etc..