The Central Processing Unit

Central Processing Unit (CPU) or (Microprocessor)

Learning Objectives

You will learn to:

·         Describe the purpose of the CPU

·         Describe the function of the CPU as fetching, decoding and executing instructions

·         Describe how common characteristics of CPU’s such as clock speed, cache size and number of cores affect performance.

Teach-ICT.com Link

http://www.teachIct.com/gcse_computing/ocr/212_computing_hardware/cpu/miniweb/index.htm

Task 1 Definition

In your note book/electronic notes describe a CPU.  Make sure that you include the following:

All computers contain a processor (PC, mobile phone, tablet, Raspberry Pi, etc.) http://en.wikipedia.org/wiki/File:Intel_80486DX2_bottom.jpg

The CPU has lots of “legs” to provide connections to the rest of the computer and they often have a heat sink to remove the excess heat.  Why do CPUs get hot?

That processors are made of transistors. A transistor is an on/off switch controlled by an electric signal.

That inside the CPU there is a silicon sheet containing thousands of transistors.

http://blog.worldbook.com/2012/03/09/single-atom-transistor-built/

Task 2 Manufacture

The manufacture of CPUs is a fascinating process involving photographic etching on a wafer of silicon. Manufacture of CPUs is not part of the specification but, is worthwhile watching the following videos:

http://www.youtube.com/watch?v=F2KcZGwntgg

http://newsroom.intel.com/docs/DOC-2476)

http://www.youtube.com/watch?v=RHAso1yM-D4

Task 3 Clock Speed

You need a definition of clock speed.

The clock speed of a CPU is how fast the transistors are switched. The faster the clock speed the faster the computer can perform calculations.

Show the Royal Institution lecture ‘Breaking the speed limit’ which demonstrates just how fast computers are:

http://www.youtube.com/watch?v=FTpdAjre8LU (7.00 – 11.04 minutes)

It is the processor clock that sends out a pulse at regular intervals. The clock speed is measured in frequency (cycles per second) using the units hertz.

One hertz is one cycle per second. CPUs are so fast they are measured gigahertz (GHz). A 2 GHz clock sends out 2 billion pulses per second. Explain that at each clock pulse an instruction is executed in a CPU.

Activity

Draw the “ON” and “OFF” sequence showing the clock cycles:

Task 4 Transistors

The number of transistors on CPUs has been increasing: http://en.wikipedia.org/wiki/Transistor_count.

That more transistors closer together mean that more calculations can be performed more quickly.

Point out that the switching of transistors generates heat. To help pupils understand how, run an unplugged whole class activity.

Activity

Your teacher will run this activity. The instructions are here for information only.

Resources

·           A class of pupils

·           A room such as a hall or an open space

·           On/off card

Explain that the class is going to act out the role of transistors in a CPU. When they are on they stand up (show ON) and when they are off they sit down (show OFF). (This works best if they are on the floor not on seats).

The pupils should stand apart from each other (stretch arms out so they cannot touch each other). Show the ON and OFF cards slowly to start with, then speed up. Ask how warm the class is feeling (they should be getting warmer just like a CPU).

Then explain that more and more transistors are being placed closer together to make computers faster and able to perform more calculations.

Get the class to stand closer to each other. Then repeat the process getting faster and faster. Ask how warm the class is feeling now.

This demonstrates how CPUs generate heat from the switching of thousands of transistors.

Task 5 Transistors

 Watch all of the Royal Institution lecture ‘Breaking the speed limit’: http://www.youtube.com/watch?v=FTpdAjre8LU and then answer the following  questions. (

1.     What is a semi-conductor?

2.     What is a transistor?

3.     Why are “bunny suits” used when manufacturing microprocessors?

4.     What is meant by parallel processing?