1. Lesson Objectives A note about notes: Aims
To understand the two main CPU architectures in use today
To be able to define and compare RISC and CISC
A note about notes:
We will not be holding your hands in lessons. You are more than capable of working out when you should be making a note of things as we go through a lesson.
If something is truly essential to copy down you will see this symbol:
Otherwise, use your common sense, make notes on things and ask questions to fill out the gaps in your understanding.

2. Recap
Von Neumann Architecture

3. The Harvard Architecture

4. What’s the difference?
VNA – All program instructions and data are held in the same memory
These are both transmitted down the same data bus, meaning that an instruction and piece of data result in two fetch requests and cannot be read at the same time
HA – Data and instructions are stored in separate memory banks and have separate buses meaning instructions and data can be fetched in the same clock cycle

5. RISC and CISC
Everything in computing is a trade off between:
Simplicity/Complexity
Speed
Power Consumption
Time
Efficiency
There is no perfect balance

6. Instruction sets
An instruction set is a list of commands that a CPU is capable of carrying out
If it’s not in the instruction set, it cannot be done…
…in one step!
This doesn’t mean a large instruction set is always better!

7. (a copy is in shared if the link breaks)
Task
(a copy is in shared if the link breaks)
10 minutes to summarise the information from the above link
You can do this in pairs or groups but your notes must be individually complete

8. CISC The CPU’s in PC’s and Mac’s are CISC based chips
This means they have a Complex instruction set
These CPU’s contain many specific instructions that speed up/make easier the use of multimedia, graphics, sound and more recently physics
The more complex an instruction set, the more expensive it is to develop, the more complex the design is and the higher the power consumption will be

9. RISC
Find out:
What RISC means
What it’s advantages are
What types of chips use a RISC today and any popular devices they are in
Why does a RISC lend itself to pipelining?
RISC processors are capable of performing the same tasks as CISC processors – how?

10. CISC V RISC CISC RISC Large (100 to 300) Instruction Set
RISC
Large (100 to 300)
Instruction Set
Small (100 or less)
Complex (8 to 20)
Addressing Modes
Simple (4 or less)
Specialised
Instruction Format
Simple
Variable
Code Lengths
Fixed
Execution Cycles
Standard for most
Higher
Cost / CPU Complexity
Lower
Compilation
Simplifies
Processor design
Complicates
Software

11. Parallel processing
We saw in previous lessons that CPU’s can be sped up through pipelining and increasing the number of cores
Parallel processing is when multiple computations are carried out simultaneously to solve a problem.
Some problems lend themselves really well to this kind of processing, others do not!

12. Using your book and the internet, find out:
Task
Using your book and the internet, find out:
What Parallel processing is
What SIMD and MIMD stand for and how they work
Examples of problems that suit parallel processing
Examples of problems that cannot be solved in parallel
Good link:

13. Review/Success Criteria
You should now be confident that you know:
The differences between the Von Neumann and Harvard architectures
The difference between RISC and CISC instruction sets
The advantages and disadvantages of RISC and CISC
The definition of Parallel processing
For next lesson you must:
Find out what a GPU is and how it can be used to make money from nothing…