Von Neumann Architecture (Edexcel GCSE 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 

• It is known as the stored program concept, storing both programs (instructions) and data in the same memory (RAM)

  

Main Memory

Why do you need main memory?

• A computer needs main memory because access times are considerably faster than secondary storage

• This means the time taken to complete operations such as the Fetch-Decode-Execute Cycle is dramatically reduced 

• Main memory holds the data and instructions that the CPU needs to access whilst the computer is turned on

• Due to the fast access times, main memory is used as short term, working memory

• Performance of main memory means a much higher cost which limits the amount that is used

• For example, RAM is commonly purchased in 16 or 32 gigabytes whereas secondary storage such as a hard drive is in terabytes

What is RAM?

• RAM (Random Access Memory) is main memory that is directly connected to the CPU and holds the data and instructions that are currently in use

• RAM is volatile which means the contents of RAM are lost when the power is turned off

• For the CPU to access the data and instructions they must be copied from secondary storage

• RAM is very fast working memory, much faster than secondary storage

• RAM is read/write which means data can be read from and written to

• In comparison to ROM, it has a much larger capacity

What is ROM?

• ROM (Read Only Memory) is main memory that holds the first instructions a computer needs to start up (Bootstrap)

• ROM contains the BIOS (Basic Input Output System)

• ROM is a small memory chip located on the computers motherboard

• ROM is fast memory, much faster than secondary storage but slower than RAM

• ROM is non-volatile which means the contents of ROM are not lost when the power is turned off

• ROM is read only which means data can only be read from

• In comparison to RAM, it has a much smaller capacity