How does a magnetic tape work?
One of the most used approaches to store data(even very big data)is using magnetic tapes. Yes! the same as music tapes or videotapes! Like any type of tape, there are two reels which turn around and pull the tape.
The tape itself is actually very simple. It consists of a thin plastic base material, and bonded to this base is a coating of ferric oxide powder.
Iron oxide (FeO) is the red rust we commonly see. Ferric oxide (Fe2O3) is another oxide of iron. Maghemite or gamma ferric oxide are common names for the substance. This oxide is ferromagnetic which means in the exposure to a magnetic field, it will be magnetized permanently.
That ability gives magnetic tape two of its most appealing features:
· You can record anything you want instantly and the tape will remember what you recorded for playback at any time.
· You can erase the tape and record something else on it any time you like.
The basic idea behind any tape is the electromagnet that applies a magnetic flux to the oxide of the tape. The oxide permanently “remembers” the flux it sees. A tape recorder’s record head is a very small circular electromagnet with a small gap in it, Like the picture below:
This electromagnet is tiny — perhaps the size of a flattened pea. The electromagnet consists of an iron core wrapped with wire, as shown in the figure.
when writing, at the gap, magnetic flux forms a fringe pattern to bridge the gap (shown in red), and this flux is what magnetizes the oxide on the tape.
Hold on! Why is there a gap on the bottom of the head?
In a nutshell because if it is enclosed, the magnetic flux will be so low. Thus, no changes will happen to the magnetic field of the medium (tape).
But yeah let’s dig deeper!
First: What is the difference between Magnetic Field and Magnetic Flux?
The most significant difference between the magnetic field and the magnetic flux is that the magnetic field is the region around the magnet where the moving charge experiences a force, whereas the magnetic flux shows the quantity or strength of magnetic lines produced by the magnet.
Second: if it is enclosed, we will have a transformer core. Not a solenoid
Third: Doesn’t a transformer core have magnetic flux outside of it?
Well, ideally no! but what the hell is ideal in this world? So yes, it does! Just as in the electrical case, there is a magnetic field outside the iron core, but no electrons are there to join the army, so not much flux results. The small flux that does go this way is called leakage flux. Leakage flux is important in transformers.
Seriously! How does it write on the tape?
Each of the individual magnetic particles on the storage medium has its own magnetic field. When the medium is blank, the polarities of those magnetic fields are normally in a state of random disarray.
When a drive’s read/write head generates a magnetic field, the field jumps the gap between the ends of the U shape. Because a magnetic field passes through a conductor much more easily than through the air, the field bends outward from the gap in the head and actually uses the adjacent storage medium as the path of least resistance to the other side of the gap.
You can think of it as that every single particle in this world goes for an easier, more comfortable way.
As the field passes through the medium directly under the gap, it polarizes the magnetic particles it passes through so they are aligned with the field. The polarity of the magnetic field (and with that the polarity of magnetic flux) can simply change by the change in the direction of the current in the coil.
but what about reading?
So now we have a tape whose particles have been magnetized and we want the head to read it for us. This time, there is no current given into the coil but there are magnetized particles that can induce a current in the coil by the change of the flux.
There are a few ways that magnetic flux can change:
A change in magnetic field magnitude, the surface of A, or the angle between B and A.
In our case is the change of angle between B(magnetic field) and A(the head). Since the polarity changes so the flux changes too.
when the polarity of flux changes, when the angle changes, this change of flux leads to inducing a current in the coil. Whether positive or negative current which depends on the polarity of flux.
Thank you for being patient and reading it thoroughly. If this article helped you understand how magnetic tapes work, please hit the like button or if you’re such a nice person, leave a comment below :)
Sources:
Upgrading and Repairing PCs (17th Edition)
https://electronics.howstuffworks.com/gadgets/audio-music/cassette3.htm
