The Von Neumann Model

Computers today show you a clean interface for you to use all its functions easily and intuitively. There is no need to type commands in a terminal (unless you’re into that), or manually flip switches in your computer’s circuitry to get it to do something you want. 

You may have heard, however, that computers can only really understand 1’s and 0’s. Have you wondered how your computer turns such seemingly jumbled numbers into something usable? One of the main frameworks that makes this possible is the Von Neumann Model.

What is the Von Neumann Model?

It is not an exaggeration to state that this model is fundamental to the design of all computers today. It is essentially a blueprint describing how computers work, specifically how the central processor connects and communicates with memory, input, and output to execute a program. 

(GeeksForGeeks, 2018)

Components of the Von Neumann Architecture

The components of the model form the core system of how your computer executes instructions.

Central Processing Unit

• The Control Unit (CU) controls the flow of the program, such as where to write data and which control signals to send (GeeksForGeeks, 2018). 

• It contains the Program Counter (PC), also called the Instruction Pointer on Intel systems. This stores the memory address of the next instruction for the computer to execute. When the program moves to the next instruction, it uses the PC to access the instruction in memory.

• The Control Unit also contains the Instruction Register (IR), which stores the 1’s and 0’s that make up the instruction the computer is executing. These 1’s and 0’s are also called Machine Code or Machine Language (ML).

• The Arithmetic Logic Unit (ALU) is in charge of operations such as adding, multiplying, bitwise AND, and bitwise NOT.

• General Purpose Registers (GPRs) temporarily store data to be operated on by the computer. It is much faster to operate on data in here rather than accessing data in memory to operate on them every time, since memory operates on a different speed from the CPU.

• The Memory Address Register (MAR) and Memory Data Register (MDR) are key to interfacing with memory. The MAR contains the address of a memory slot to be accessed, while the MDR contains the corresponding data of that memory slot to be read or written.

Memory

• Memory, as its name suggests, stores the data and instructions required by the program.

• Memory contains a certain number of “memory slots”, which each have an address used to access the slot.

• Each address slot has a fixed number of 1’s and 0’s it is able to store. This number multiplied by the number of “memory slots” makes up the total memory capacity of the device.

• The CPU interfaces with memory using the MAR and MDR, which help read data from or write data into memory.

Input/Output (I/O)

• These are external devices connected to the computer, such as your screen and keyboard. Your screen displays the output of a program, such as the result of adding two numbers, while your keyboard is used to tell the computer which two numbers to add.

• Since these devices, referred to as peripherals, operate at a different speed than the CPU, special methods are needed to communicate data between them and the CPU.

Conclusion

Though the Von Neumann Model formed the foundation for the earliest of computers, it is just as relevant today in illustrating how modern computers work, by illustrating the relationship between the CPU and its components, memory, and input / output peripherals. 

Reference List

GeeksforGeeks (2018). Computer Organization | Von Neumann architecture. [online] GeeksforGeeks. Available at: https://www.geeksforgeeks.org/computer-organization-von-neumann-architecture/ [Accessed 31 Mar. 2025].