Von Neumann Architecture

• The Von-Neumann Architecture is also called "Princeton Architecture".
• Von-Neumann Architecture consists of CPU, Memory Unit, Buses, and I/O Devices.
• It follows the concept of a stored-program computer, in that instruction data and program data, are stored in the same primary memory in the form of binary digits.

Main Functions of Von Neumann Architecture:

• In this architecture, one data path or bus exists for both instruction and data.
• As a result, the CPU does one operation at a time and Uses a single processor only.
• Executes programs in the Fetch-Decode-Execute cycle.
• It either fetches an instruction from memory or performs read/write operation on data, one at a time and in order (serially).
• The processor decodes and executes an instruction, before cycling around to fetch the next instruction
• The cycle continues until no more instructions are available
• So an instruction fetch and a data operation cannot occur simultaneously, sharing a common bus.
• This design is still used in most computers produced today.

Components of Von-Neumann Model:

1] Central Processing Unit (CPU)

2] Memory Unit

3] Buses

4] I/O Devices

1] Central Processing Unit (CPU)

• The CPU is responsible for executing all the bulk of data and programs in a specific manner.
• It is an electric circuit responsible for executing the instructions of a computer program.

• It consists of an Arithmetic and Logic Unit (ALU), Control Unit (CU), and various registers.

  • Arithmetic and Logic Unit (ALU) - Performs the required micro-operations for executing the instructions. Eg. Arithmetic & Logical Operations.

  • Control Unit (CU) - The Control Unit consists of a program counter that contains the address of the instructions to be fetched and an instruction register into which instructions are fetched from memory for execution. It also controls the operations of ALU, memory and input/output devices, buses.

  • Registers - It is a high-speed storage area in the CPU. The data processed by the CPU are fetched from the registers.

2] Memory Unit

• A memory unit is used to store all the data and information in a storage system permanently.
• The memory stores binary information in groups of bits called words.
• The internal structure of a memory unit is specified by the number of words it contains and the number of bits in each word.
• It is the place where the computers hold data and programs which are in use.
• It is a collection of storage cells together with associated circuits needed to transfer information in and out of the storage.

• Memory units consist of two types as follows:

  • Primary Memory - It includes RAM (Random Access Memory) which is volatile.
  • Secondary Memory - It includes ROM (Read Only Memory) which is Non-volatile.

3] Buses

• The bus is a communication system that is used to connect the computer components from one part to other parts of the system.
• In buses information is shared between the registers in a multiple-register configuration system.
• A computer bus is either parallel or serial.
• A bus structure consists of a set of common lines, one for each bit of a register, through which binary information is transferred one at a time.
• Control signals determine which register is selected by the bus during each particular register transfer.
• Von-Neumann Architecture is comprised of three major bus systems for data transfer as follows:

4] I/O Devices

• Input/Output device is a Hardware device that is used to communicate with a computer.
• An input device is used to provide data to a computer for entering data and program in a computer system.
• Examples of Input devices are a keyboard, mic, mouse, joystick, etc.
• Output devices receive information from the computer and carry out the data that has been processed by the computer to the user.
• An Output device displays information on the screen (monitor) or the printer.
• Examples of Output devices are monitors, printers, headphones, etc.