https://www.youtube.com/watch?v=HA96GwuvdVM

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

performanceKeywords: CPU, Cache, Fetch-decode-execute, clock speed, dual-core, quad-core.

Lets play cards!

CPU

Data CacheInstruction Cache

RAM

Storage Device(Backing store)

InstructionsData

Inside the CPU

The CPU can only process one simple instruction at a timeEach instruction is

‘Fetched’, ‘Decoded’ then

‘Executed’The speed of the

fetch-decode-execute cycle is

determined by the clock speed

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.

Imagine the process like this:

Multi-Core processors

Core 1 Core 2

Individual Cache

Individual Cache

Shared Cache

CPU 2 processors

= Duo

4 processors

= Quad

Some tasks can be done

much quicker with

multiple processors

To prevent writing to the same location, each core needs its

own cache.

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 i7i3 = Duo

I5 = Quad

i7 = Quad (but can seem like more

due to ‘clever stuff’!)

Which computer will give the better performance?