CPU Architecture
Computer Science: OCR A Level, topic 1.1.7
Von Neumann Architecture
Von Neumann architecture is still used today in everyday electronics like personal computers (PCs).
Von Neumann architecture
- The main architecture that we use today is the Von Neumann architecture.
- It was designed in the 1940s by John von Neumann.
Programs
- The architecture works on the stored program concept:
- A program must be stored in main memory to be executed.
- Its instructions are fetched one at a time and executed serially.
Units, registers & buses
- The Von Neumann architecture uses:
- One control unit.
- One arithmetic logic unit.
- Five registers.
- Three buses.
Harvard and Contemporary Architecture
Other CPU architectures exist, which are specialised for different purposes.
Harvard architecture
- Harvard architecture has two memory locations, one for data and one for instructions.
- The instructions are often unchanging so will be kept in Read Only Memory (ROM).
Uses of Harvard architecture
- Harvard architecture processors are mainly used in digital signal processing applications such as:
- Medical body signal monitoring.
- Sonar.
Contemporary architecture
- Although modern PC processors are still based off the Von Neumann architecture, they often have elements of Harvard architecture and other elements for efficiency.
Differences to Von Neumann
- The cache inside a modern processor is split into two storage locations for data and instructions and these are accessed using a Harvard style system.
- Processors now also have multiple cores and pipelining which further improve efficiency and capabilities of modern processors.
Test yourself on CPU Architecture
In which decade was the Von Neumann architecture invented?
How many buses are used in the Von Neumann architecture?
What is the stored program concept?
Which features of modern processors improve the efficiency of the CPU?
Where are instructions kept in Harvard architecture CPUs?