2. The Central Processing Unit
Lesson Objective: Understanding the CPU
Learning Outcome:
Define the keywords
Describe fetch-decode-execute
Why Cache is preferable to RAM
How clock speed and cores affect performance
Keywords: CPU, Cache, Fetch-decode-execute, clock speed, dual-core, quad-core.

3. Lets play cards!

4. CPU Instruction Cache Data Cache RAM Storage Device (Backing store)
Instructions

6. Inside the CPU
The CPU can only process one simple instruction at a time
Each instruction is ‘Fetched’, ‘Decoded’ then ‘Executed’
The speed of the fetch-decode-execute cycle is determined by the clock speed

7. The CPU clock speed The speed is usually measured in GHz (GigaHertz)
1 GHz = 1000 Million cycles per second
Think of this happening for each step of the fetch-decode-execute cycle.

8. Imagine the process like this:

9. CPU Multi-Core processors 2 processors = Duo 4 processors = Quad
To prevent writing to the same location, each core needs its own cache.
Core 2
Some tasks can be done much quicker with multiple processors
Individual Cache
Individual Cache
Shared Cache

10. i7 = Quad (but can seem like more due to ‘clever stuff’!)
Core processors
In the exam you may be given specifications like this: 1.2 GHz Duo Processor
In real life you will see specifications like this: Intel 2.5 GHz Core i7
i3 = Duo
I5 = Quad
i7 = Quad (but can seem like more due to ‘clever stuff’!)

11. Which computer will give the better performance?