Introduction

Recap the last lesson, ask the class can anyone explain in their own words how a computer can represent an image as a binary number?

What’s the difference between data and information? Data is the raw material, the numbers that computers work with. A computer converts its data into information (words, numbers and pictures) that you and I can understand.

 

 

Where can we store data?

Discuss what the children know about data storage devices, if you can, collect some examples of storage devices, old and new, to look at and compare:

 

Which one of these holds the most data? Why do you think that? 

Establish that the size of the physical device is now no longer an indication of how much data it holds. Compare a 1.4 MB floppy disk with a (much physically smaller) 8GB SD card. 

Floppy disks were common in the 1980s for storing computer data, for example, computer games came on them. Today we use SD cards in things like digital cameras to store the photos. How many of these floppy disks do you think you would need to have the same amount of data storage space as the SD card?  Almost 6000! (5851)

Or compare a CD, DVD and Blu-ray, which all look physically very similar but have very different storage capacities.

 

CD

700MB

 

DVD

4.7 GB

1 DVD = approx 6 CDs

 

Blu-ray

25 GB

1 Blu-ray = approx 5 DVDs or 35 CDs

 

Cloud storage is an even stranger concept to understand as there isn’t anything to physically see. So what is cloud storage?  This video explains it really well:

 

 

but it means when you save your data online, via a website or app. When you do this you are saving data to servers belonging to web companies, such as Google or Microsoft, which could be anywhere around the world. 

What are the advantages of Cloud storage? Cloud storage has the advantage that the data isn’t saved to one physical location, so there’s nothing that you could break or lose (like a DVD or USB stick) and you can often access your data from different devices, any place, any time as long as you have an internet connection, so you don’t need to worry about remembering to pick it up (like a DVD or USB stick). Does it have any disadvantages? You are usually reliant on having a web connection to access your data, also, some people have concerns about privacy and security of saving your data on servers that belong to these companies, we need to trust them to look after our data and respect it.

 

How does a computer store data?

So now we know different options for where we can save our data, and we know that our data is converted and saved by a computer as binary code.  Computers do the clever bits of reading and converting this data from binary code to the form in which we want to view it. 

This video from code.org explains more about this process and also recaps some of the other learning from our previous lessons.

 

 

So it's the CPU (processors) that reads and processes this data. Different CPU chips work at different speeds. Manufacturers are always releasing more powerful chips that can process more data at faster speeds. 

Show the students the How computers store and process data worksheet. This requires them to explain the process that was shown in the video in their own words. It's been broken down into 6 steps, with a couple that are harder to explain done for them. 

 

 

The process is as follows:

 

Step 1 - INPUT

You press a key on the keyboard. This is an input device and sends a signal to the computer

Step 2 - INPUT

The letter you press is detected and converted in a number. Every character that is typeable on the keyboard has its own special ASCII number  This number is then converted to a binary code which is sent to the CPU.

Step 3 - PROCESS

Next, the CPU calculates how to show the letter you have pressed as pixels.

Step 4 - PROCESS / STORAGE

The CPU checks the memory to find the algorithm (instructions) for how to draw the letter you have pressed. 

Step 5 - PROCESS / STORAGE

The CPU runs the algorithm for drawing the letter that it has retrieved from the memory. It stores the shape that’s created as pixels in the memory.

Step 6 - OUTPUT

The pixel information is output to the screen as binary code. The screen converts the binary into pixel colours to display the letter on the screen.

 

... and this all happens in a fraction of a second! 

 

How is an electrical signal turned into code?

We’ve discussed that computers deal with everything as binary code, and that this code is transmitted by electrical signals. The final step in this unit is to try and understand a little more about how that happens, don’t worry if your head is hurting a bit by this stage! . 

Modern CPUs contain millions or billions of individual transistors that are microscopic in size. Transistors act as a switch, which can be turned on or off.

 

 

If a transistor is on it will pass an electrical signal which is interpreted as a 1 in our binary code. If a transistor is off it will not pass a signal, which is interpreted as a 0 in binary code. 

So the on/off pattern of the transistors and the electrical current that flows through them is how the binary message is sent and received by the CPU. 

There are many many circuits inside a computer that can be combined to complete lots of different tasks. Have a look at this video from code.org to find out more about how they process binary data and perform calculations, among other things. 

 

 

So the key to how a computer processes and stores binary code are transistors and how they manage the flow of electricity passing through them. The circuits manipulate the signals created by the transistors to perform tasks.

 

 

Plenary

To finish, let’s see what you can remember from the last few weeks.

• What makes a computer a computer? (a computer in general is any device that accepts input, processes it according to a stored program, and produces an output.)
• What’s the difference between computer hardware and software? (hardware is the physical parts of a computer and peripheral devices that can be connected to the computer. Software is any set of instructions that tells the hardware what to do. It is what guides the hardware and tells it how to accomplish each task.
• Can you remember what some of these terms mean? Explain them to someone. (see lesson 3 for definitions)
  • Hard drive
  • CPU
  • GPU
  • ROM
  • RAM
• What are these numbers in binary code? 1010 (ten) 1111 (fifteen)
• What is the smallest unit of measurement for digital data? (1 bit)
• How is binary code converted into an image? (a number that represents the colour of each pixel (how much red, green and blue) is converted into binary and output to the screen, telling it how to display the image.