Computer arch: How is processor connected to Memory?

Computer architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer systems.  Wikipedia

So computer architecture show how the system works, how every thing is connected to others.


In this article we talk about the different architecture based on memory connection to CPU.

There are two different models:

  1. Von neumann architecture
  2. Harvard architecture


 Von neumann architecture

has only one bus which is used for both data transfers and instruction fetches, and therefore they can not be performed at the same time.

Harvard architecture 

has separate data and instruction buses, allowing transfers to be performed simultaneously on both buses.


What is the best model Von neumann or Harvard ?

What is the best” is always a wrong question, “What is better” is a suitable question based on the system’s requirement that you design.

What arch. MCUs and Processors use?


Von neumann is used in Processors because, unlike MCUs, processors don’t have internal memory or peripherals  and the connection to memory is through external bus and        Von neumann is sutiable because:

  1. Cost: less buses means less cost.
  2. Space: we don’t need to waste large space of motherboard.
  3. Processors mainly deal with only one memory, RAM which holds the data and instructions, so only one bus will be suitable and the slow access will be substituted by the high speed of the processor and using the cash memory.


Harvard architecture is used in MCU because:

  1. MCU contains everything on the chip. RAM, flash, and peripherals  and due to the small size using multiple buses is not an issue.
  2. MCU speed is not high so multiple buses will help with the limited speed of MCU.



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