Magnetic Storage

Another technology that I find pretty amazing and kind of wild to study is magnetic media.

Here are some examples of magnetic media. Here I have a hard disk drive. Here's tape from a tape backup system. Here's a floppy drive, and that's the material, that's the magnetic material that we copy the data onto, right in there. And then here is a tape drive, a cassette tape that a lot of times we just store music on, but there are times I have stored data on these as well.

North and south

The first thing to understand about magnets is there's a north side and a south side to a magnet. The north side we're going to represent as red, and the south side we're going to represent as blue. So here we have a magnet, and this magnet has a north side, the red side, and a south side, which is the blue side.

But one of the interesting things about magnets is that opposites attract. So if I were to take the blue and try to align it with the blue, watch what happens. I'm going to get it close, and the blue gets repelled and the red gets attracted to it. So it's one of those cases where opposites attract: the north is attracted to the south side, and vice versa.

I've got this device right here that's going to help us measure this magnetic field. You can see it has a red and blue side as well, so it's a magnet with a red side and a blue side, and it swivels. So what I can do is bring this close, and notice now the red is following the end of this blue. It's attracted to that blue, so it's following it around to be close to that blue. But what happens if I move this to the other side is that the red gets repelled and the blue takes over, and now the blue wants to face this red side. So we can flip this back and forth just like that.

Now, really what this is demonstrating is that we can measure a magnetic north and a magnetic south with this, and that's pretty key to how magnetic media works. So what I can do is create a tool that reads what the direction of a magnetic field is. Is it going from south to north? We can represent that maybe by a zero. Or is it going north to south? We can represent that by a one.

Changing a magnetic field

The next thing that I want to cover is that we have some control over this magnetic field. What we have here is a screwdriver, and then over here is a screw, and the screwdriver is not magnetically attracted to this screw at all. You can see that it doesn't do anything. What I have here is a device that I can roll over the top of this screwdriver right here, so I'm just going to go back and forth, and now what happens is I can pick up this screw with this screwdriver. We've created a magnetic field on this screwdriver.

Now I also can come back and put it through one of these other holes and go back and forth with this, and now it's no longer magnetic again. So I can change the magnetic field of this screwdriver. Since I can change the magnetic fields of the screwdriver, I could change it in one direction to represent a zero and another direction to represent it as a one.

Storing bits on the media

Now imagine taking some material from the screwdriver and applying it into something that is a really thin strip like this. Now what we have is, we can divide this up into little sections, and then we can do a north/south on each one of those little sections, and that would represent a bit.

Now imagine that this line here represents that tape. What we're going to do is divide that tape into little tiny sections here, and each one of those is going to be a bit. They're not even on there, but in actual media it's going to be evenly spaced. And then we create a magnetic pole on this tape in one direction or another, and one of those is going to represent a one and the other one is going to represent a zero. And now we have a way to store that data.

Here's a little better example of that, where we've got this all split up into these sections here and we've got these directions that are happening here. So in this case, maybe this is a 1 1 0 0.

The read/write head

Of course, we both have to read this and also write it. So what we have here is a read/write head. The read/write head has some sort of magnetic coil on here that creates a magnetic field that would then make that direction on here happen. It also can go back and then sense, be able to read, what direction that is. So here's the read/write head that can both write and read the data from this, if it's a disc or tape or whatever the case may be.

So in the end here we have all of these directions on here that we have, and this read/write head can sense that, and now we have these ones and zeros that are going to translate into our pictures or our documents or whatever.