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After reading this answer to the question How long can a floppy disk spin before wearing out?

... one could see thru the floppy... Not just badly worn, but the magnetic coating was outright polished away, all the way to the transparent carrier film.

And after taking a closer look to the floppy drive heads:

Floppy Drive Heads Floppy Drive Head

I was wondering: If the data is stored on a magnetic disk then why are the drive heads apparently so close to the disk that they touch and create friction with the disk? As I imagine that friction is the cause of damage to the disk resulting in a degrade of the disk over time. Why aren't the drive heads at least for example 2-3mm away from the disks? Wouldn't using stronger magnets in the drive heads compensate for the greater distance and result in a frictionless floppy disk drive (FDD)? Would this not drastically increase the lifespan of floppy disks as it would be frictionless?

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    You might like to have a look at the answers to this question, especially the comments on tofro's answer regarding sleeve to media friction. Jan 15 at 11:12
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    But you could eliminate that sleeve friction by making the material not floppy ... oh. Jan 15 at 12:48
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    This seems to be again a question about basic physics, as the information asked for is all about basic knowledge of magnetic fields and their behaviour. It might be better asked at Physics.SE.
    – Raffzahn
    Jan 15 at 15:03
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    Because the floppy disk was developed as a cheap medium. Flying heads require rigid surfaces with tight tolerances, which is therefore not cheap. Jan 15 at 18:01
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    @TobySpeight people often joke about these being non floppy and it's clear the disk inside is but I'd not made the connection that this name isn't retained for historical reasons but because disk medium rigidity is a major engineering decision point and trade off because, in part, of the friction vs self support issue, and probably also head tolerances. Jan 22 at 21:25

2 Answers 2

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TL;DR:

"Frictionless" Floppies are called Hard Disks (*1), consisting of a hard media platter and a head in distance of the media (flying or otherwise)

Floppies are 2D tapes. While slower than tapes, their advantage is in (faster) random access for small data sets. The construction was made to save on tapes. They were never intended for continuous operation over long time. They are short term storage and exchange media optimized for low cost storage of small data sets for quick exchange.

Friction is reduced by picking the right materials and shape for head construction as well as low friction coatings for the disk.

Not to mention, that head friction is only a very tiny part of wear compared to the friction applied by the sleeve of a floppy (Hint: friction is applied over area - low friction over large area may give way more wear than higher friction in a small area (*2))

Also, friction is only one part of wear, as the media gets constantly warped when moved under the head.

The way to extend lifetime is to simply stop the floppy when not in use. Works quite well.


why are the drive heads apparently so close to the disk that they touch and create friction with the disk?

They are not apparently close, they touch it permanently.

A floppy is the same technology as a tape. It's in the name, they are a flexible media running along a head.

They are intended to be lower cost than hard disks (*1).

As I imagine that friction is the cause of damage to the disk resulting in a degrade of the disk over time.

That's why it's called 'Spanabhebende Datenverarbeitung' roughly 'chipping data processing' ;))

No difference to tapes. A floppy is a rotating 2D tape.

Why aren't the drive heads at least for example 2-3mm away from the disks?

Because than they wouldn't be able to detect the magnetic flux changes. IIRC the magnetic field weakens quadratic, that is, doubling of the distance results in a quarter of the field.

A floppy head gap is positioned way less than a micrometer away from the magnetic source. Turning this into millimeters means making it several thousandfold. In turn the picked up signal will be many million times fainter to make up for this the magnetization must be stronger and at the same time further apart from any change. In the end a 5.25 inch flopp may only hold a few hundred bits.

Wouldn't using stronger magnets

Stronger magnetic fields make bigger bits. Double the magnetic field means quadrupling the bit size.

Would this not drastically increase the lifespan of floppy disks as it would be frictionless?

Stronger magnets would make them useless.

Also, it still would not be friction less, as air does as well have friction. That's the reason why high end fixed disks are filled with helium - an air composition of less friction than the usual 70% nitrogen.


Now, there are floppies with 'flying' heads: Bernoulli drive.

These were floppies with a head positioned a few micrometers away. This was not done to extend life time but speed and capacity. Bernoulli drives rotated about 10 times faster(~3000 rpm) allowing density and transfer speed in regions comparable to fixed disk drives. The media was still warped, but this time upwards due the 'suction' of the Benoulli effect.


*1 - Read carefully: HARD disk, not FIXED disk. A hard disk is one where the media is not flexible. A fixed disk iswere the media is not changeable (*3). Fixed disks are usually hard disks, but hard disks are not always fixed disks. Common use of Hard Disk when talking about a Fixed Disk is simply wrong.

*2 - Yes, if a floppy is read only at a single track at all times this will be visible, but not because head wear is higher, but because the track will suffer from sleave and head wear.

*3 - Or more correct, where media and head mount are in a non seperable unit.

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    We just called them "disks" until floppies were invented, at which point "hard disks" became a necessary term. (See also "black and white television"). Jan 15 at 18:03
  • Aside: OTOH, there were tapes that were "disks": TU58 DECtape II. It used pre-formatted tape cartridges with two tracks, each containing 256 512-byte blocks and supported random-access. Quite the slow boot device for a VAX 11/750.
    – HABO
    Jan 15 at 18:57
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    The original was the LINCtape, reborn as the DECtape. DEC reused the honorable DECtape name for the TU58. Jan 15 at 19:47
  • Atlas may have been the first to use addressable tapes. I added an answer to this question about random-access magtapes. Jan 15 at 20:05
  • Note that "fixed disk" is also inaccurate, as fixed disks may or may not be removable. Nomenclature gets twisted any way you look at it, and the one that seems to have won is a "hard drive" is something that would typically be in a fixed disk position, but doesn't have to be. A "hard DISK drive" has solid platters, as opposed to a floppy disk or solid state drive. "Spindle drive", "platter drive", and "spinny disk drive" are other retro-defined terms to be specifically not solid-state, hard drives.
    – MichaelS
    Jan 16 at 2:45
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The head gap must be very narrow to be able to make sharp magnetic transitions on the moving magnetic media. It also means the magnetic field does not bulge out too much out from the head so the media must move very near the head. If the gap was larger, it would bulge out more, but be weaker and it could not make sharp transitions on the media, which means less data can be stored.

So it makes sense to make the heads very smooth and polished so they have very little friction. If the heads and floppies do get dirty with dust, the dust can scratch the head and then the head can scratch the floppies.

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  • Sorry, but that logic is flawed. The head gap is not in relation to speed, but flux change density. It defines how far two changes must be apart to be separated. Vulgo, gap size is bit size.
    – Raffzahn
    Jan 15 at 23:21
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    @Raffzahn I never said it was related to speed and can remove the word about speed. But now that you mentioned it, surely gap size and media speed must both be parameters among many other things that define how densely data can be stored.
    – Justme
    Jan 15 at 23:49
  • Speed is a function over time, as well is applied magnetic field when writing, thus time can be eliminated from the equation. Same goes for reading. Of course does faster media movement mean shorter signals and the need for faster electronics, but that doesn't make it a main influence on head design.
    – Raffzahn
    Jan 15 at 23:57

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