How Magnetic Storage Works

to like holographic memory storage. And magnetic storage has played a really important role in the history of technology in general and computers in particular. So I want to focus on how magnetic storage works. Who came up with that idea and even dive into the science of magnets. Yes, insane clown posse, I'm looking at you. We're gonna discover how magnets work. So if you've been wondering since that

video I got, I got your hook up. So first, let's talk about why magnetic storage was a necessity in the first place. So how do you preserve information so that you can access it again later? Because in the old days, and I'm talking like tens of thousands of years ago, verbal communication was where it was at you stored all that information up in your head. Someone would tell you something important and you had to remember it. Perhaps they would tell you within the context of a story.

And then eventually, if you were trying to preserve information, you would tell that same information to someone else and pass it along. This way, this is essentially folklore. That's

how knowledge was maintained for centuries. And then way back in the day, someone said, hey, what if we made up some symbols to represent these sounds we're making to communicate with each other, and then we put those symbols into some sort of fixed format, like in a clay tablet, And that way we can preserve the information a lot longer.

And if Bob, who's really good at making fires, can explain how to make fires, and we we put it down in this format, we'll be able to make fires even if Bob does something stupid like walks off the edge of a cliff or something. And writing was born. It probably went a little differently from the way I explained it, but I think I got the gist of it. Not everyone, however, was a fan of this development. Believe it or not. There were people who were against the

whole idea of writing stuff down. Socrates was actually a critic of writing stuff down, or at least that's what we hear, because Socrates didn't write anything down, his students did. Uh. He said that the written word is fixed, and therefore it can't defend itself or any arguments it makes, so it's inherently flawed. If someone writes down an argument and your access to the argument is in that written format, and you have questions or you have attacks on that argument,

it can't defend itself. The person who wrote it could if they were there, but if they're not there, then the argument has to stand on its own, and therefore it has to be less effective. Let's say that an actual human being. He also said that if you write stuff down, you don't have to remember it yourself, and that makes you less intelligent, because if you're not actually

committing something to memory, you're getting super dumb. Uh. This might sound a lot like some of the arguments people have made about Google and the Internet, and it's absolutely correct.

Every single time we have created a new way to permanently store data in some form or another, people have brought up this idea that it's making us more dumb, Like they might say, hey, Back in the day, you'd have to remember all your phone numbers, like all the numbers of the friends and family that you would be calling a regular basis. But now it's all on your phone, so you don't remember it. You may not be able to rattle off more than two or three phone numbers

today because of that, therefore you are more dumb. I don't subscribe to that particular argument. I think having the accessibility of information outweighs the fact that we are no longer able to remember it necessarily. Uh. The point I would make is that comprehension is always more important than being able to recall something. You might be able to recall some information, but if you don't truly comprehend it, it's no It's of no use to you. So I

don't think it's necessarily a measure of intelligence. It's certainly, perhaps more of a statement about our memories than anything else. But I'm getting off on a tangent here. So I think the developments we've had have been phenomenal. We wouldn't be where we are today if we were still depending upon just telling each other the important stuff and hoping that they would be able to then tell other people the important stuff we just told them and in way

that was accurate and effective. We clearly wouldn't be where we are today if we still depended upon that. And I don't have to travel all the way across the world to find a specific guru to learn how to perform a particular skill. I can just go onto YouTube and watch like thirty or forty videos until I find

one that actually makes sense. So that's progress. Take that, Socrates. Now, throughout history, we saw many advances in the way we store information, and as we developed more advanced technology, it became clear that a compatible method of storing data would be really handy. So imagine what computers would be if

they could not save information, they'd be practically useless. You need to have a way of storing data somehow, whether it's in magnetic storage, optical, solid state punch cards, whatever. You need something that can record the information otherwise it's

only good for a moment. And a lot of folks worked on this problem, and as is the case with many technological developments, some of that work had nothing to do with computers, but more with researching fundamental scientific questions and finding answers to questions lead other people being able to use that information in practical ways that we didn't anticipate. And this is kind of another soapbox I like to get up on, uh to argue for the importance of

exploratory science. Applied science is really interesting. Applied sciences when you're trying to find a particular solution that will work for some sort of problem. Right your you might be researching whether or not a specific material would be great to use for a particular purpose, like bulletproof material something

like that. But exploratory science, when you're not necessarily looking for applications, is also important because we expand our knowledge about how the universe works, and it can open up opportunities to leverage that knowledge in ways we could not have anticipated when we first started looking into the issue in the first place. It's in and stuff, So I argue that exploratory science needs to continue to be supported. Let's uh now acknowledge all this, take a deep breath,

and get ready to jump into the strange world of magnetism. So, first, magnetism, or more specifically, electro magnetism, is one of four fundamental forces that govern the atomic behavior in our universe. So the other three if you're keeping track, are the strong nuclear force, the weak nuclear force, and gravity, And if you want to rank those from the weakest to the strongest, you'd start with gravity. Gravity is negligible at the atomic scale.

It's there, but it's so faint as to be almost absent. And this is largely because gravity is dependent upon mass, So at the atomic scale, mass masses are so small there's barely any gravitational attraction between particles. But gravity is kind of nifty because while it's weak, it is there. And in fact, there's a gravitational pull on every bit of matter from every other bit of matter in our universe.

So you, that is you listening to me right now, you are are exerting a gravitational pull on the Sun, and on Alpha Centauri, and on the Andromeda galaxy. You are exerting a gravitational pull on everything else that is matter in our universe. It's just that that gravitational pull is so weak as to be practically nothing, but it is there. So since gravity is something we ourselves can and do experience in our daily lives, we categorize it as one of the familiar forces. Now, next in the

rank from weakest to strongest, is the weak force. Now that's responsible for nuclear beta decay and some other decay processes. And this one's pretty difficult to explain. And since I'm are you going to have to explain magnetism, I'm gonna call for a pass on this one. Let's mulligan it. But this is a force that we do not experience firsthand in our daily lives, So this one actually falls

into the category of unfamiliar forces. Now next in strength, so second strongest if you prefer, is the electromagnetic force, the one will be focusing on today. Now, this is a force that exists between all particles that have an electric charge. So electrons, for example, will bind to a nucleus because electrons have a negative charge, and a nucleus, which only contains positively charged protons and neutral neutrons, is net positive. And you know that opposites attract, so we

have the negative electrons attracted to the positive nucleus. We can and do experience electromagnetic forces on a daily basis, so this one is one of the familiar forces. And then we have the strongest of them all, all the strong nuclear force. This is the force that holds a nucleus together it's a dominant force in various chemical reactions, and it has to be strong because it's doing something that's really difficult to do. It's holding together similarly charged particles. Remember,

a nucleus is a bunch of protons and neutrons. The protons all have a positive charge. They don't want to be and when I say want, I don't actually mean they have motivations, but they don't want to be next to each other. Those parts, those similar charges are repelling one another. So the strong nuclear force has to be stronger than the electromagnetic force in order to hold protons

together in a nucleus with a bunch of neutral charge particles. Ah, it does have a very short range, however, so while it's stronger than the electromagnetic force, it does, the range does not reach very far outside of a nucleus, so we do directly observe it in our daily lives, and therefore it is an unfamiliar force. So gravity and electro magnetism are familiar forces. The strong and weak nuclear forces

are unfamiliar forces. Uh So what makes electro magnetism tick and how did we even figure out how to make good use of it? Well, let's start by imagining a bar magnet. A lot of this is going to go back to stuff that you probably learned in elementary school, middle school, high school, those physics courses, that kind of stuff, basic science. So you've got your bar magnet. Uh, let's just say it's a rectang. It's rectangular in shape. So you know you've you've got uh, your north pole and

your south pole on the magnet. Um this these represent the various charges, magnetic charges of the magnet, opposites tracked. So if we were to bring this bar magnet close to another bar magnet, the north end of our bar magnet would start to exert a poll on the south end of the other bar magnet. Or if we were to try and bring the north pole of our magnet close to the north pole of the second magnet, it would push against each other, just like I was mentioning

a second ago. Now, magnets produce a field around them that we can represent as lines of force, and those lines exit from the north pole, loop around the magnet and enter the south pole. A permanent magnet is always producing the sort of magnetic field. It's it's consistent, it doesn't waiver. Um. You may hear about things like electromagnetism.

I'll talk a little bit more about in a in a bit, where you have to move a coil through a varying magnetic field, will a permanent magnet creates a consistent magnetic field unless you start doing things like moving it around, in which case you're really just moving where the magnetic field is. You're not actually fluctuating the field itself. Now, inside a magnet a permanent magnet are microscopic regions called magnetic domains, and each of these domains is essentially a

tiny magnet with its own north and south pole. Only by aligning the poles of all of these uh magnetic domains in a similar direction, like north south, will you get a permanent magnet. So if you could just zoom in on a permanent magnet, you would see all these tiny regions that are essentially magnets that are all aligned

the same way north south. If you didn't do that, if the alignment was mixed up so that you had, you know, an equal mixture of north south and south north, they would cancel each other out and you wouldn't have a magnet. It would just be inert magnetically speaking. So, uh, that is something that's interesting because you can actually do that to magnets in a couple of different ways. I'll talk about that in a second. So all of that is changeable. Bomb bom bomb. I wrote that in my notes.

Actually I had to say it. I could show Dylan, but he's working on something else. By the way, when all those magnetic domains are aligned north south, what happens if you were to cut the magnet in half right between the north and south pole. So imagine you've got this rectangular bar magnet. You've got you've labeled one in the north pole, the other in the south pole. You cut the magnet in half horizontally across, well, you would

end up with two magnets. The middle of that magnet would become the south pole for the north end and the north pole for the south end. That's because those magnetic domains I was talking about, those tiny regions inside the magnet themselves itself, those are all aligned north south. So if you cut the magnet across, you still have those magnetic domains lined up north south, so the overall

magnetism is preserved. You get two magnets for the price of one, but don't cut into magnets magnets, they tend to be at least the ones that we typically use for things like our fridges and stuff are ceramic magnets, and they don't cut so well unless you have like a a diamond saw, which some of you probably do. And and if you cut magnets normally, then disregard my warning. I'm talking about people who don't typically do that sort of thing. If you are going to do it, where

eye protection because that stuff can shatter anyway. Uh, if you do that with the magnet. Essentially, each magnet has approximately half the magnetic domains of the old magnets, so they're not particularly you know, the the individual magnets aren't as strong as they were when they were a single magnet.

Because you're you're magnets, You're overall magnet strength is dependent upon the accumulative effect of the magnetic domains within it, all right, So each of those magnet domains are tiny magnets. There are three ways to get them to line up so that the overall material becomes a magnet itself. Like how you get them all to line up like north south? So way number one is to whack on it with

something heavy, which isn't a joke. If you hold the material in the north south direction and strike it with a hammer, you physically realign the magnetic domains and you can knock the material into a weak magnet. There's a bit more to it than that, but that's the basic idea, and that that does mean that you're not going to get a very strong magnet as a result, but you can physically force those magnetic domains to be in the

same direction and create a magnet that way. Way number two is that you can place the material inside a strong magnetic field and make sure the material is in the north south alignment and you just leave it there and if it's a strong magnetic field, it will start to realign the magnetic domains within your target material so that they gradually line up with the magnetic fields direction. So you just have to have a strong enough one to affect the magnetic domains in your target material and

then eventually you end up with a magnet. So that's kind of cool. And way number three is yes, zap it with electric current. So one hypothesis is that this is how loadstone, which is a naturally magnetic material you can find here on Earth, was originally formed the ideas that loadstone, which is made up of this stuff called magnetite. Uh, some of it was struck by lightning over the the the millennia that Earth was forming. So you have magnetite

on the surface of the planet. Occasionally lightning strikes and hits some of this magnetite and then magnetizes it. That was That's one hypothesis. But there's another one which suggests that magnetite gained its magnetic properties during the time when Earth was forming, and it was through more of a just a physical uh, the physical process of cooling where these magnetic domains aligned in the proper way. Here's the thing, we don't really know how it all got started. We

don't have that information. No one was around back then to write it down or put it in magnetic storage. So it's still a bit of a mystery. But we do know that those are two possible ways that this could have come about. And uh, you can also render magnets inert by changing the alignment of the magnetic domains within it. If you heat a magnet up beyond its cury point, which is different for different magnetic materials, it loses its magnetism. The heat warps the material and makes

the magnetic domains fall out of alignment. So what used to be magnetic will no longer be. So something that would stick to your fridge no problem, will just slide off and hit the floor, and everyone will be sad, unless you just did it as a scientific experiment, in which case you might be happy that you've got the result you expected. Now we can experience magnetism because of electrons.

This time, negatively charged sub atomic particles hold the key to whether a material is affected by magnets or isn't. You know, might wonder like, why are some things magnetic and some things aren't? Why do magnets stick to some materials but slide right off of other materials? And ultimately the answer falls with electrons. Now, electrons orbit the nucleus right in the atoms. You remember your basic description of an atom, where you have a nucleus at the center

and electrons orbiting at different orbital shells around the electrons. Typically, electrons will pair up with other electrons. You'll get pairs of electrons. They have a state that's called spin, and each electron in a pair has the opposite spin of its partner. So we can describe spin as up or down. For example, if one electron is spinning up, the other

one by necessity has to be spinning down. You cannot get both electrons in a pair to spin in the same direction in the same orbital That just that ain't cricket. It's part of the quantum mechanical principle we call the poly exclusion principle. And until I did a research for this show, I could have sworn that referred to the practice of non inviting Polly shortier parties. So I guess you've learned something new every day. That got a smirk from Dylan. It's maybe he'll laugh when he listens to

it the second time. Uh. Some elements have an unpaired electron in an orbital just because that's just how it works out. So those unpaired spinning electrons generate a very tiny magnetic field, and we call it an orbital magnetic moment, which sounds like something you'd expect in a romantic science fiction film. Iron, for example, has four unpaired electrons that all have the same spin. Those four unpaired electrons have an orbital magnetic moment. So magnetic moment has a magnitude

and the direction, which means it is a vector. The bottom line is this vector refers to the strength of the magnetic field and the torque it can exert. So a permanent magnets magnetic moments are composed of all the moments of its atoms. In other words, you've got all these atoms that represent an orbital magnetic moment because of the spin of the electrons of the unpaired electrons. If you've got enough of them and they're aligned the right way,

that determines the permanent magnets magnetic moments. So iron and several other magnetic elements have a crystalline structure, right, so think of it like scaffolding. It makes this very ordered kind of structure as opposed to something that looks much more chaotic. So as iron cools from a molten state, atoms line up into this crystalline arrangement, and groups of atoms that have a parallel orbital spin will line up within the crystal and those form those magnetic domains I

mentioned earlier. The qualities that make good magnets are also the same ones as the qualities that make materials attracted to magnets. So a strong magnet will attract iron and other elements that have these orbital magnetic moments in alignment. Now, not all permanent magnets are equal. The ceramic magnets you may have on your fringe door a pretty weak all things considered. They're made of a mixture of iron oxide

and a ceramic composite. These are ferric magnets, that's what we call them, ferric for the iron that's in them. But on the other end of the scale are neodymium magnets, a rare earth element magnet there is much much stronger than the ferric magnets we tend to use, and they typically contain a mixture of neodymium, iron and boron. They could be really strong too, uh, I have played with somewhere. If they get into contact with something like a metal table,

it can be really hard to remove them. We had some here at how Stuff Works that were potentially causing injuries. Uh. One person slipped one in their pocket and then found themselves stuck to a filing cabinet for a little bit. Uh. This was way back in the day, but it was one of those things where a lot of us didn't have a whole lot of experience with it because at the time they were fairly uncommon. Today you can order neodymium and other rare earth magnets online without much trouble.

But when I started um, first of all, how stuff works was easy because there are only three things, so it was easy to explain how stuff works. Once you wrote the three articles, you were done. But over time more stuff was made and we had more work to do, and at that point it was more. It was more uh uh, well, it was easier to get ahold of

neodymium magnets at that point. Now, some materials are called temporary or soft magnets, and those will produce a magnetic field in the presence of another magnetic field and retain some of that magnetism for a while after they leave the field itself, so they're very easy to LUNs. So imagine that you've got something like a paper clip and you put it within the range of a magnetic field for a while, and it starts to have its magnetic

domains aligned according to this magnetic field. You remove it and you find you can pick up other paper clips with it, but only for a little while, and then it stops working. That's that's very typical with soft or temporary magnets, they very quickly will change, but then they will over time change back to being, let you know, not magnetic. But if they're also hard magnetic materials, these it's harder to change them, but then they will stay

changed for longer. So stuff like iron, if you're able to really realign those magnetic domains and iron magnet will hold that magnetic ability much much longer. And that's how you can end up with permanent magnets as opposed to some that will just temporarily be magnetic. Um it's kind of interesting. Uh. So then you've got electro magnets and this will only produce the magnetic field in the presence

of electricity. And I'm sure everyone listening to this has done some variation on the the experiment where you take an iron nail and you coil some wire around it, usually some insulated copper wire around the nail several times, uh, and then you run an electric current through the wire and you create an electro magnet. The nail becomes magnetic and you can pick up all sorts of stuff with it. The strength of the magnetic field is dependent upon the number of coils around the nail as well as some

other factors, but that's the primary one. Uh. And UH, you know it's it's a cool, little basic science experiment you can run, but it's also the basis of a ton of the work done in electrical fields, including general electronics, computers, storage. It is an important fundamental piece of technology. UH. And the very simple applications of this you can find in

stuff like electric transformers or electric motors and dynamos. Like transformer, you can have two different coils of wire, one that is got a lot more coils to it, uh, like maybe twice as many as the second one, And when you run a current through the the larger number of coils, the magnetic field it generates induces electricity to flow through the second set of coils, but steps down the voltage because you have half as many coils around a core as you do with the first one. Uh. That's how

you can step down or step up voltage. And that's why alternating current ends up being much more effective for distributing electricity across the distances than direct current, because you can't do that with direct current. You need that alternating electric current in order to create the magnetic field that will induce electricity to flow through a separate set of coils.

Just like you need a varying magnetic field to induce electricity, you need that varying electricity to produce a varying magnetic field. It's this interesting relationship, a fundamental relationship in our universe between electricity and magnetism. And uh, that's why I was saying before. If you have a permanent magnet and you just put it next to a coil of wire, it's not going to induce electricity to flow apart from when you first introduce the magnetic field to the coil, because

it's not varying. You'd have to spin the the permanent magnet, which would uh, you know, effectively, according to the coil's perspective, change the alignment of that magnetic field. That would induce electricity to flow through the wire. But just having a standard magnet staying perfectly still next to wire, you don't get the electricity to flow that way. And that is a very important aspect to memory storage as well. And

that's our lesson on the physics of magnets. Without diving too deeply into quantum mechanics, I think we're ready to talk about our use of magnets with electronics. But first let's take a quick break to thank our sponsor. All right, we're back, and we just learned how magnets work in general, But when did we figure out they could be useful

for storing information? So I'm gonna skip over all the historic uses of magnets leading up to data storage because I cannot spend another hour talking about compasses, or ironically, i'll lose Dylan here in the studio. So in the late nineteenth century we saw a boom in innovation that was mid to late nineteenth century was a crazy time in the world really for inventors discovering not just fundamental principles of science, but how to apply them in technology.

I'm talking about stuff like Samuel Moore successfully sending an electrical signal that could be decoded into communication, all the way up to Alexander Graham Bell showing that electricity could also be used to carry audio signals and then be converted from electricity back into audio signals. That really got things moving. And over at Thomas Edison's Menlo Park, a guy named Oberlin Smith got a gander at a cylinder phonograph and got some interesting ideas. So first let's talk

about this cylinder phonograph. It would record sound by transforming audio waves into electrical signals. That would then cause a needle to etch grooves into a wax cylinder. So you've got this wax cylinder. It would slowly spin, a needle would be dragged across it, and as sound came in, it would cause the needle to wiggle around and that

should cause variations in the etching on the wax cylinder itself. Now, when you took that cylinder out and you put it in another phonograph and you placed a needle on it, uh within the groove and he started to earn the thing the cylinder, the needle would start to shake because it's following the groove that was made by the previous recording. Essentially,

that whole process would be reversed. The shaky needle would generate an electrical signal which would then go to a essentially a speaker a diaphragm and cause it to vibrate and that would generate the sound. So you would get a replica of the sound you made when you were speaking into the wax cylinder phonograph. Now, Oberlin Smith wondered if he might be able to do the same thing, only instead of using a wax cylinder, he would record sound onto magnetic wire, not ape, not a disk, but

an actual length of wire using magnetism. Now, he was not successful in this attempt, but he published his ideas in a journal called Electrical World in eight and ten years later a Dutch inventor inventor named Valdemar Poulson gave it another go. He began a working magnet recorder. He started building it. He called it the telegraphone Poulson, and he filed a patent for this invention in eighteen nine. So one year after he started working on it, he

showed it off at the nineteen hundred Paris Exhibition. So how did it work? What exactly was it doing? How was it preserving this audio information in a magnetic format so that it could be played back? Well? Paulson knew that he needed a magnetically hard material. If you remember what I was talking about before the break, that's a material that we're retain its magnetic moment indefinitely. It may very gradually revert back to its original status, but it

will hold it over a great deal of time. And if you want to record data for later retrieval, obviously you want to make sure that that data remains intact. Otherwise you have a self destructing or at least a self erasing message on your hands. So Poulson had to experiment with various factors to make certain he could record anything to the medium. To begin with, if the medium has a coercivity factor that's very high, that means you have to use stronger magnetic fields to affect it. I'm

always talk about magnetic fields. Now I'm thinking about the Book of Love. It's great song by a group called the Magnetic Fields. Back back to this. So you have to have a really strong magnetic field in order to affect that material, and uh, that can be difficult. It can start to eat in on your efficiency. And you need the magnetic information to be distinct enough so that

you could get a would replay signal. And uh, you know, when you're reading the material back later, you want to make sure you can actually hear what was recorded and not just get some sort of muffled you know, simulation of the of the sounds you made. So to record information onto a wire, you first need a recording head. You need something that's going to generate a magnetic flux that can affect the medium you're using the wire in

this case. This, by the way, is also true for other methods of magnetic storage, including cassette tapes, VHS tapes, floppy disks, and some hard drives. When I say some hard drives, I mean magnetic hard drives. Obviously there solid state hard drives that are not affected in this way. They don't use that that technology, they are not part

of this discussion. So the recording head is a transducer, and basically a transducer is something that converts some physical quantity into an electrical signal, or as the reverse, So you might have a transducer that can measure pressure like air pressure and change that into an electrical signal. That's a transducer. But in this case we're talking about things like a microphone a transducer, and a microphone converts pressure

from sound waves into electrical signals. With recording devices, you can use one transducer to pull double duty one of them. It can act as both a recording head when recording, so it's it's actually writing something to the storage medium, or it could be a read head when playing a signal back. It's reading the signal and then converting it back into whatever it was originally before it was stored

in that format. Now these days, most recording devices still use that are still using magnetic storage, have a dedicated recording head and a dedicated read head so that each transducer can be optimized for its respective role. You don't see a whole lot of them where it's doing both things. Uh. Some very cheap electronics, probably because then you don't have to have as many components in It makes it less

expensive to produce. Now, the right head's job, or the recording head if you prefer, is to convert electric current into a magnetic field. But you remember what we said about electro magnets, that's pretty easy to do. The field it generates needs to be strong enough to affect the storage medium, the wire, but also it has to fall off quickly as you move away from the recording head. In other words, you don't want the effect to be widespread in area, or else you're going to end up

affecting way too much wire at once. You'll end up with having to use way more wire to record very short sounds. In this case, and not only is that inefficient, but you'd also run the risk of writing over stuff you've just recorded. Let's say that you're writing something to wire. If the magnetic field is wide enough so that it's constantly overlapping what you just corded, then all you're really

doing is muddling your recording with every successive sound. So a coil of wire creates the magnetic field when electricity runs through it. This wire is coiled around a soft magnetic material. Remember those are the kinds of magnetic materials that are easy to influence. But then we'll go back to their natural state shortly after the magnetic field they've

been exposed to has gone away. This creates what we call a magnetic flux, and it concentrates at the tip of the soft magnetic material that's the core of this coil. A common design for early recording heads was a ring that had a small gap cut into it, and then you would wrap the wire around the inside of this ring, like you know around the ring. So imagine just a regular ring. You cut a little gap at one end. On the other end, you've wrapped this this coil of wire,

and you run electricity through it. Turns the ring into a magnet, but the gap creates a difference in this magnetic field. The soft material, the soft magnetic material, conducts magnetic flux easily and the gap doesn't. This causes the magnetic flux to do something we call fringing. It fringes. A fringe field is a bit tricky to explain, but it's easier to understand if you imagine a horseshoe magnet. So the two ends of the horseshoe are the two poles,

the north pole and the south pole. The fringe field is the magnetic field that extends outside the space between the two poles. That would be a fringe field. Now, that fringe field is what the right head uses to actually record information onto the magnetic medium. Now, with sound, we're talking about an analog approach, meaning you'd find a smooth variability in the medium. You would create that by

varying the magnetic flux in subtle ways. The record warding head adjust the magnetic flux by varying the current running through the head and the recording medium thus has a variability in the magnetic flux recorded within the wire itself. The wire represents a sort of copy of the flux. If you were to run the wire back. So let's

say you've got the red head. The transducer acts as a red head, and you run the wire next to it uh sequentially, so you're just spinning one reel pulling wire across so that this red head is very close to it. That would create a varying magnetic field across the gap in the red head, and that then would create a varying magnetic field in the core of the red head, which would induce a current to flow through the coil of wire, which then could be sent to

an amplifier. The varying electric electrical signal goes to a transducer such as speakers, and then it can play back the sound. Now, those old wire recorders moved at a pretty good clip. A post war wire recorders would play back wire at about twenty four inches per second, so

two ft a wire per second. That's about sixty one per second for you folks on the metric system, if you wanted to record an hour's worth of audio, you would need seven thousand, two hundred feet of wire or about two thousand one of wire, and you could only record along one direction of the wire. So if you want to listen to it again. You don't have to wind all the wire back up into a reel and then play it out across a reed head all over again.

Most of these early ones were hand cranked too, so you would get variability on the sound quality as it was played back, plus when you were recording, so it took a steady hand to create a decent recording and a decent replication. And if you wanted to rerecord over it. Let's say that you've you know, you recorded an hour of someone catterwauling, and then you're like, well, that wasn't really worth it. I would love to use this wire

to record something else. You would first have to run that wire by a strong permanent magnet, and that would effectively erase the stuff that was on it before, because the strong permanent magnet would cause all those uh, those those magnet magnetic domains inside the wire to realign to

the permanent magnets magnetic field. It essentially erases all the variability, all the flux that was copied there before and turns it back into a uniform medium which you then could run through and record stuff on again the same thing. By the way, it's true for lots of other magnetic storage media. Now, eventually Poulson began to work with other types of magnetic media, and a big breakthrough came with

the invention of plastic. I say the invention of I really mean the mass production of plastic has been around for a pretty a long time, but I'm talking about when we really started producing it on a mass scale. So you can use plastic film coated with a ferro magnetic powder. This is how cassette tapes, VHS tapes, even floppy disks work. You can make a cheap recording medium

this way. Uh, the invention of the cassette tape itself was another big jump because engineers figured out how you could double the amount of material you could record on a tape if you just recorded on half of it at a time. Now, this is a little tricky to explain without the use of visual aids, but I'll try and give it a shot. So imagine that you've got

a length of flat ribbon in front of you. You might think of cassette that cassette recorders are actually putting information on both sides of the ribbon, but that's not what is happening. All the information for side A and side b are on one side of that ribbon, but they are one hundred and eighty degrees opposite each other, side by side. So you lay out the ribbons so it's horizontal in relation to you. You're looking at a horizontal strip of ribbon. Imagine a line going down the

middle of that ribbon horizontally. The top half of the ribbon is one side of the cassette and the bottom half is the other side of the cassette. So when you put a cassette into a cassette player, the reed head is positioned over just one half of that tape and it reads what's off of that. When you flip the cassette over, then the side of the tape that's running across the reed head is the opposite of of that.

You know, it's the bottom of the ribbon as opposed to the top of the ribbon, and that's all you're able to listen to side b uh. So that's kind of cool, I thought. Now, next, I'm gonna talk specifically about using magnetism to store information for a digital computer, which is a little bit different from what I've been chatting about so far. But first, let's take another quick break to thank our sponsor. All right, So in the last section I talked about how magnetic recording can create

a variable magnetic flux for analog playback. But what about computers. Computers rely on binary language, not analog. It's not a variability, it's a collection of zeros and ones. You have to describe computer information in this format as either a zero or one. Ultimately, when you get down to it, every computer language out there, once you get down to the very basics, ends up being translated into zeros and ones because computers just don't deal with these variable fields. So

how do you get it to do that? So, while the format is more or less obsolete, I'm gonna talk about floppy disks for a bit, and that's because there are a lot of parallels between floppy disks and cassette tapes, which I talked about in the last section. Floppy disks, by the way, used to come in several sizes. When I first started using computers, the standard size in the

US was the five and a quarter inch disc. There were larger discs that came before that, but the first ones I ever used were five and a quarter inch. A lot of people thought they were called floppy disks. Because the outer sheath of the disc itself was flexible. Some people even thought you could fold them up and put them in your pocket, which technically I guess you could do, but you wouldn't be able to use them later because you mangle the disk inside and it would

no longer spend properly inside a computer. So don't do that. Later on came the three and a half inch discs, and these had a hard plastic casing, but they were still floppy disks because the disk inside, the actual medium upon which information was stored, was still this flexible material. A lot of folks thought that these three and a

half inch discs were actually hard disks. They said, you know, the floppy disks were the five and a quarter three and a half Because the plastic it is sturdy, that's a hard disk. No, that's not a hard disk. But anyway, that's all ancient history, and you guys probably don't even understand what I'm talking about. Get off my lawn, all right. Inside the outer covering of these discs was the actual disc itself. We call the floppy disks that, but they're

not disc shaped. If you were to show someone a floppy disk and they had absolutely no context for it. They knew what the word disc meant. They take one look at and say, why the heck do you call it a disc. It's because on the inside there is a disc of material, and it is essentially a plastic

base that's coated with ferro magnetic materials. And the advantage of this is that if you apply a magnetic field to it, it would record that information permanently, or at least until you erased it and wrote over it, or if you encountered a really strong magnetic field, and it was a really fast way to record a lot of information.

So disks are organized into concentric rings. You can kind of think of an old vinyl album in the same way how the grooves slowly move inward on the um on the disc, But in this case their actual concentric rings of information, not not just one line that slowly,

you know, swirls inward towards the center. So when a computer is reading information back, it can it can reference some information at the at the front of the disc and learn exactly where a file is located, and it can then position the read right head directly over the appropriate part of the disc, rather than having to go through the whole thing sequentially. So with the cassette tape, if you want to listen to a specific song, you

have to wait. You mean, you can use fast forward to speed things up, but you can't jump straight to the track you want to hear, unlike you could with say, compact disc. Well, in this way, a flop disc is more like a compact disc in that a computer can understand exactly where the file is stored within those concentric rings and go straight there. In other ways, it is very different from a compact disc, but in that specific

way it is similar. Now in other words, it's kind of like lifting a record player's needle off of one groove and skipping ahead to a specific song on an album, lowering the needle and then playing it, and thank goodness record players are coming back. So that you guys know what I'm talking about when I say these things. This, by the way, is a type of direct access storage, meaning the computer can get direct access to that information

in a very short amount of time. When writing to a disc, first the drive will use in a race coil, and this essentially just clears a section of the storage medium for writing. So it's it's kind of like exposing that steel wired to a permanent magnet. It's that same principle. You want a clean slate to write upon, and typically this clean slate is a bit wider than the actual

right section you're going to be working on. You want the area that is a clean slate to be larger so that you have a buffer zone at either end, and that way it keeps adjacent files from interfering with each other. If you were writing information to that part of the disc and it went over that area, you would start writing on top of some other file and then the storage wouldn't work at all. So the right head puts data on the disk drive by applying one

of two magnetic fields to the tape. It either aligns the magnetic material as north south or south north. That means it's either a zero or a one. Like so imagine that north south magnetization represents a zero and ou

north represents a one. The right head can then go through this disc very very quickly, applying these magnetic fields one after the other, maybe several North south in a row followed by a south north or whatever, and it is recorded on the disc itself, and when you read it back then you know by looking at the code, Oh these are you know, three zeros in a row and then a one. It replicates those zeros and ones

that were recorded to the storage medium. This, in a way is much more simple than a variable magnetic flux because you only have to have two magnetic states. You just have to have something that represents a zero and something that represents a one. No other values are accepted, so you just have to have those two basic modes, and the same basic principles apply to other computer magnetic storage. Magnetic hard drives use a very similar approach to the

ones I described for floppy drives. And you probably heard that it's a bad idea to expose computers to strong magnetic fields, and the big reason for this is that magnetic storage. If you bring a strong permanent magnet close enough to magnetic storage media, you'll erase the data that's stored there. That includes data that's on a hard drive if it's a magnetic drive, right, if it's a solid

state drive, it's a different story. Or if you were to take a strong permanent magnet and threatening someone by by holding a compact disc with all their photos on it, and you're saying if you come any closer, I'm going to ruin your pictures by putting this magnet up to the c D. It won't work because the information stored on the CD is an optical format, not magnetic, and magnets aren't going to affect it at all, so you shouldn't be doing that anyway. It's kind of a jerk move,

but it wouldn't work, is what I'm getting at. So in future episodes I plan on exploring stuff like optical storage and how that works, how is it similar to and different from magnetic storage? And also solid state drives, which are you know, pretty much the standard and a lot of different computers these days, which have incredible advantages in how quiet they are and how fast they are, but they tend to be a lot more expensive than

your old style magnetic drives. I'll talk about those in future episodes too, And if you guys have any questions about the stuff I mentioned here, feel free to send me an email. My address is tech stuff at how stuff Works dot com, or you can always drop me a line on Facebook or Twitter. The handle of both of those is text stuff H s W. And I will talk to you again really see for more on this and thousands of other topics. Is it how stuff works? Dot com two