Lesson video

Hey there and welcome back to the computer systems unit.

I'm Mac, your computing teacher for this unit.

In this lesson, we're going to take a deeper look at optical and magnetic storage.

To prepare yourself, you're going to need a pen and a notepad to take notes while you're learning and I'd also like you to remove all distractions from around you.

This includes your mobile phone.

As per usual, I've got my bottle of water here so you make sure you got some refreshment if you need it throughout the lesson.

If you'd like to pause the video here and get everything you need, I'll be here when you get back.

In this lesson, you are going to explain how optical storage works, you're also going to explain how magnetic storage works and then we're going to look at comparing storage devices at the end of the lesson.

In lesson five, you learned about solid state storage which stores data using electronic circuits.

In this lesson, we're going to have a look at the other two types, optical and magnetic.

Let's start by having a look at optical storage.

Optical storage devices use discs with a reflective surface to store data.

The name should give you some clues as to how these devices work.

What does the word optical make you think of.

Hopefully, the picture was a bit of a clue for you, but let's see if you've got it right.

We're going to jump right into a task and you're going to complete a fill in the blanks exercise.

If you head up to your worksheet, there is a statement for you to fill in with some words that are at the bottom of the slide.

You can either write them in yourself or drag the boxes into the right place.

If you want to pause the video here and go do that, I'll be here when you get back and we'll go through the answers.

Welcome back.

Hopefully you found that okay.

Let's have a look at the answers and then I'll talk a little bit more about how optical storage devices work.

So, the first sentence is, optical storage devices use what to store data? They use light to store data.

A laser burns marks into the reflective surface of the disc.

These marks are called pits, and the gaps between them are called lands.

So the word optical should have made you think of vision or seeing or light, and that is how these devices work.

They use light to store data.

A small laser will burn tiny marks into the reflective surface on the back of a disc and these marks are called pits and then the gaps between them are called lands and this is what represents our binary data.

You can see an example here of an optical storage device.

This is inside the reader that you would put the disc into.

You can see the little blue mark, that is the Laser.

To write data the disc will spin on top and the laser will burn pits into the reflective surface.

And then to read data, the laser is shown at a lower intensity and then the reflection is measured.

A light sensor reads the light that's reflected back from the laser.

The pits do not reflect light so the bits where it's burnt do not reflect lights and the lands do.

That being said, I've got another fill in the blanks activity for you to have a go at.

If you want to pause the video here and head back to your worksheet and use the words available to you to complete the sentences.

Resume the video when you're done and we'll go through the answers.

Welcome back again.

Hopefully you found that one Okay, we're just trying to see what binary data is represented by these pits and lands.

So on an optical storage device binary data is represented as follows.

When the laser is over a Land, the sensor reads a one.

As I said, lands reflect light so if the sensor detects light is going to read a one.

If the light hits a pit, then a zero is read.

So this is a lack of reflection so if the sensor picks up light, it's going to read a one, if it doesn't get any light back, it's going to read zero.

So, to sum up, optical storage devices are small and robust if they properly stored.

Obviously, the reflective surfaces quite easily scratched and the data can be damaged in this way that's why you have to be really careful when you take CDs out of a player to put them back into the cases 'cause otherwise you might ruin the data that's on them.

These discs tend to come in three formats, as a read-only which is ROM has very similar names some of the memory devices you learnt about in lesson four.

There's wright once which confusingly has the moniker R that means that because they can only be written once for most of the time you're only reading from them, so they just use the R for read.

Then you have rewritable discs which have the moniker RW.

Even the rewritable discs have a limited lifespan, it can't be infinitely burned and then flattened out and then burned again.

On the right hand side here, I've got some possible advantages of optical storage.

I'd like you to pause the video here and have a think about which of these you think would be an advantage of optical storage.

Right, let's have a look and see which of these are actually advantages of optical storage devices.

So optical storage devices are portable.

They're just small discs, and they're really lightweight, which is why they're so good for distributing things like music or video games.

They're also cheap to produce.

Again, this makes them great for distribution because you produce many of them for very low cost and they're also reliable.

If you take care of them, the data can last a really long time.

So the advantages are the cheapest capacities, extremely small and portable and they last a long time.

But the disadvantages of optical storage are that they're expensive, the large capacities if you wanted to store multiple terabytes of data actually ends up being a lot more expensive than other storage mediums. They're easily scratched if you don't take proper care of the discs.

And they can have very slow read speeds, especially when compared to things like SSDs or hard drives.

The last one is that they also have a limited amount of reusability.

Even the rewritable discs only have a limited lifespan.

This is because the laser actually physically burns the surface of the disc so there's only so many times you can do that before the disc is damaged.

If you'd like to pause the video here and take a note of these on your notepad, you really should be able to recall what the advantages and disadvantages of optical storage are.

Resume when you're done and we'll carry on.

Right, hopefully you've made a note of those.

Let's go on to the next one.

We're going to have a look at magnetic storage devices.

For this demonstration, I'm going to be focusing on hard drives.

But all the other different types of magnetic storage also work using similar principles.

Hard Drives also use discs to store data.

They're called platters and they're covered in a special material.

Sections of this material can be magnetised and demagnetized to represent binary data.

A read/write head is attached to an arm and the head will apply a magnetic field to the different sections to either magnetise them or demagnetize them.

There's two key pieces of equipment inside of magnetic storage hard drives.

A set of discs which again are called platters and an arm with a read/write head.

We're going to jump into another activity now.

If you head over to your worksheet there are some sentences on there for you to complete.

I'd like you to make sure you use the pieces of equipment in your answers.

Pause the video here and we'll go through the correct answers when you get back.

Welcome back.

Hopefully you found that Okay, let's go through the right answers and you can adjust yours if needs be.

So, to write data, the platters spin and the read/write head will magnetise and demagnetize sections underneath it.

It's important to point out that the read/write head is actually more like a fork and not a single arm.

So as it moves it will move between all the discs at once.

If you imagine the platters are sat like this, the read/write head can move over the top and it can read from different platters at the same time.

To read data, the head moves over the spinning platters and measures whether sections are magnetised or not.

So the magnetised sections represent a one and demagnetize sections represent zero.

Keeping this in mind, what do you think are some advantages of magnetic storage? I've got four options at the bottom of the slide here, I'd like you to pause the video and have a think about it and choose two of them.

Resume when you're done and I'll give you the right answers.

Let's have a look and see what the advantages of magnetic storage are.

So magnetic storage devices tend to be of a higher capacity than most others and they're also infinitely reusable.

So that cheap, a large capacities, you can get really large hard drives for a much lower price as compared to a lot of other storage devices.

They're infinitely rewritable.

If you take care of them, you can use them for years and years.

And they're reliable throughout that time.

So if you save something now and go back to it 10 years from now, as long as you've taken care of your hard drive, the data will still be there.

And they have faster read speeds than optical storage.

That doesn't mean that it's all good though there are also some disadvantages for magnetic storage.

They can be damaged if they're dropped or exposed to a magnetic field.

So the moving parts make it vulnerable to dropping damage.

So if you take a hard drive out and you throw it around more than likely one of the moving parts will stop to function.

They have slower read speeds and solid state devices, and they require a lot more power to run.

Again, this is down to the moving parts, it requires more power to move the discs and also the read/write head.

If like to pause the video here and again, make note of these advantages and disadvantages.

It's very important that you understand when you choose a magnetic storage device or another storage medium.

Resume when you're done and we'll carry on.

Well, I hope you've made a note of those and you're going to remember them.

All right, let's keep going.

For the next activity, you're going to have a go comparing some storage devices.

When you compare storage devices, you need to be able to discuss the following characteristics, the cost per gigabyte, the storage capacity, the access speed of the data, or how quickly it can be read, the durability of the devices, are they easily damaged, and things like that.

Reliability will the data still be there after long periods of time, and also their portability, can I easily take it from one computer to another.

As with most of these lessons, instead of me lecturing you on this, I'd rather you have a go here and then we can discuss the results.

So on your worksheet, you will find two things to help you do this.

One is a knowledge organiser with all those characteristics and the three storage mediums for you to fill in as we do these comparisons, and also a larger table for you to use as reference with the details of a variety of different storage devices.

If you'd like to pause the video here, and you'd like to use the reference table to rank the three types of storage in terms of cost per gigabyte.

You'd fill in the first column of your knowledge organiser with either expensive or cheap, depending on the storage medium.

Have a look through the table and see how much it costs per gigabyte for each of the different storage devices and see which one is the most expensive and which one is the cheapest.

Resume the video when you're done and we'll go through it.

Welcome back.

Hopefully found the reference table easy to get on with and also you were able to rank them but let's have a look at how we do that.

So we want to look at the cost per gigabyte of the three different storage mediums and I gave you this reference table to use.

So let's have a look through it.

We can see that the solid state storage tend to be the most expensive.

They go all the way up to three pounds per gigabyte for USB stick, SSDs are a bit cheaper but tend to come in larger capacities, and overall are not as cheap as other types like DVDs or hard drives.

Next, we have magnetic, which is cheap per gigabyte and you can get them in really large quantities.

And also optical which tend to be cheaper for small quantities but if you wanted to get a large storage capacity and might be more expensive, but I'd still put them as cheap.

So the results of our comparison are that solid state is the most expensive and it gets the label expensive and optical and magnetic, both equally cheap.

Really it depends on another comparison of storage capacity over which one you would choose.

There's very little difference between the prices of magnetic and optical storage.

Now that you've seen us rank the first one, let's have a go at doing another ranking on your own.

This time, I'd like you to have a look at the storage capacity of the three different devices and fill in the second row of a knowledge organiser with either small, medium or large.

Compare the three, see which ones have the biggest storage capacity and give that large and whichever one has the smallest, get it small, and then in the middle, you have medium.

Right, resume the video when you're done and we'll go back through it.

Welcome back.

I hope you enjoyed that comparison.

Let's have a look.

So, as far as capacity is concerned, our SSD and hard drives tend to be the largest capacity and of those two, the hard drive wins out.

So magnetic tends to have the largest storage capacities especially when compared with cost.

Solid State comes in its second with large USB sticks available all the way up to two terabytes and SSDs it can go as big as four.

The smallest by far is optical storage devices.

These ones are limited by physical size, there's only so many of those little pits you can get on a disc.

They are definitely the smallest of our three devices.

So solid state is medium, optical is the smallest and magnetic has the largest capacity.

It's important to remember that whilst both solid state and magnetic can have larger capacities, magnetic is definitely bigger and optical storage devices are by far the smallest.

So if anybody needs a small capacity obstacle is what you go for but for larger capacities you choose between the other two.

So rather than going through each one individually, I'd like you to do a bit of a longer comparison now and fill out the rest of the table in your knowledge organiser.

And I want you to apply the following labels.

So for access speed, I like it either say they're very slow, they're slow, they're fast or they're very fast.

The durability can either be robust or delicate.

The reliability is vulnerable, reliable, or very reliable, and portability can either be stationary or portable.

If you'd like to head back to your worksheet, fill up the rest of the rows in your knowledge organiser, and then we'll come and look through the comparisons in these rest of these categories.

See you when you get back.

Welcome back.

I think that one probably would have been a bit longer but hopefully you were able to sort of compare them and apply these labels when necessary.

Let's have a look at the results.

So let's start with access speed.

Which of the three is the fastest? You might remember for our deep dive into solid state storage and lesson five that is by far the fastest of the secondary storage mediums. It's not as fast as RAM but outpaces the other to by long way.

So solid state would be very fast, optical is very slow and magnetic is just slow.

You'll notice that the two other mediums involve moving parts, and so the discs physically need to be moved in order for the data to be read.

This greatly impacts the access speed of the data and add an extra component called seeking time.

If the data isn't where the read/write head is or where the laser head is, they need to spin the discs to find the data first.

This isn't a problem for solid state.

Next in the durability category, solid state devices tend to be very robust, they have no moving parts, you can drop them with very little worries.

Optical and magnetic are equally delicate, with optical being slightly more so.

That's because optical discs can be scratched, damaging the data whereas magnetic tend to just be vulnerable to things like drops or magnetic fields.

How about reliability? Which is the most reliable? So solid state suffers from solid state degradation.

Again, we talked about this in lesson five, but they have limited amount of read and writes.

Eventually the SSD will wear out, just like you heard about in the Tesla cars that save a lot of logging data.

Optical devices, if cared for, are very reliable.

They will last for years and your data will be intact.

Magnetic devices are also reliable as they will keep your data stored for long periods of time, you'll find that there are lots of servers full of hard drives that store data for long periods of time for companies and businesses.

Final category was portability.

So which of the three is the most portable? Optical is definitely the most portable as you can just pack in the disc up in one of the cases and take it wherever you want with you, you can also put it in the mail and transport it very easily.

Solid State tend to be quite portable especially if you're looking at USB sticks.

Solid state drives are built into the computer so they're less portable, but still more so than magnetic.

Magnetic hard drives have to be connected to a computer and they also need to be carefully transported so you avoid dropping them or exposing them to a magnetic field.

These categories are the important ways you need to be able to compare storage devices.

That's all for this lesson.

Thank you very much for your hard work, getting to grips with comparing secondary storage devices.

I hope you enjoyed it.

The last thing for me is to ask you to share your work with Oak National.

If you'd like to, of course, please ask your parent or carer to share your work on Instagram, Facebook or Twitter, tagging @OakNational and #LearnwithOak.

I'll see you next time, happy learning.