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3M Diskette Reference Manual (1983) [pdf]

123 pointsposted 3 months ago

41 Comments

alentred

3 months ago

Just recently I wanted to show my kids the 5.25" floppy disk - I had a small stack somewhere, but could not find it. I have finally found an 3½" floppy and have shown it to my kids (14 y.o. max). Evidently they never used such a thing, but I was genuinely surprised they didn't even know what it was. After a considerable amount of time one of my daughters hesitated but said something like: "Wasn't it like old USB stick thingy?". Given they have no USB stick either that's not bad, I guess. Then I proceeded to explain that a floppy disk is pictured on Save buttons - you just had to see their faces, it was a moment of the big revelation.

vbezhenar

3 months ago

Given that computers play a huge role in our lives, shouldn't we taught children some kind of history of computers? It's not that big anyway.

integricho

3 months ago

Since they have never seen floppy disks before, why were you surprised that they did not recognize what they were?

blueflow

3 months ago

... have they seen Save buttons with the Floppy pictured on it, either?

ZuLuuuuuu

3 months ago

Apparently 3M was a serious player back in the day on magnetic tapes and floppy diskettes. But today they are not present in a similar market (digital storage) at all.

I wonder what was it like to go through that timeframe, as the management and the employees, where the floppy disks were becoming obsolete. Did they purposefully took the decision to not pursue CD, flash memory market? Or was it just a shortsightedness of the management where they fell behind and eventually had to exit that market?

Of course 3M still managed to be successful and today it is one of the big market cap companies...

trollbridge

3 months ago

They spun it off into Imation, as 3M’s specialty is coatings and chemicals. Storage no longer really uses those things

You could say that 3M doesn’t make the things you use every day; they make the things you use better.

hammock

3 months ago

We call those “specialty chemicals” and it’s smaller volumes but much higher profit margins. Evonik (Germany) is another example.

Things like- not the asphalt shingle, not the granules on the asphalt shingles, but a COATING ON the granule on the asphalt shingle that provides weather protection.

Or, not the memory foam mattress, and not the liquid precursors that are combined to create the foam in the mattress, but an ADDITIVE to the precursors to the foam in the mattress which regulates/ensures a consistent size of foam bubbles during manufacture.

trollbridge

3 months ago

Next thing you know, you're going to tell me about this company called BASF from Germany.

hammock

3 months ago

Decent example of a basic (vs specialty) chemicals company, although they are huge of course and quite diversified, they make a crap ton (millions of tons) of basic stuff like propylene, ethylene, ammonia, methanol, etc

chiph

3 months ago

3M was indeed a big player in those markets. I purchased both 5.25" and 3.5" 3M floppies and they were good quality and reliable.

I expect they left the market because of declining use and the entrance of much cheaper foreign manufacturers. I expect they didn't enter the flash memory market as they had no existing manufacturing base for them to build on. They would have had to rebrand another firm's chips and circuit boards.

anikom15

3 months ago

They were not in the storage market. They were in the tape market. It just so happens tape was used for storage at the time (floppy is essentially tape in a circular shape).

No more tape storage, no more market for 3M.

billfor

3 months ago

It's interesting that the index hole is not on y-axis, if it is actually used to allow operations. I used all my SS 5.25" as DS just by flipping them I think, and they just worked. You weren't supposed to do that, but all the SS diskettes were coated on the other side, so you just fliped it and it would work, but it wouldn't be certified for that use case.

Tuna-Fish

3 months ago

As soon as the motors used to spin drives were able to provide a once per rotation signal to replace the index hole, the hole was no longer used for anything. The detector and lamp used to detect the hole were more expensive than using a signal from the motor.

phire

3 months ago

Motor rotation isn't quite enough, as it's not aligned to the sectors on the disk.

Drives which do skip indexing (Like Apple's Disk II) use the actual data on the disk for indexing. Each sector header has a track/sector/head ID, allowing the controller to know where it is on the disk without the need for indexing.

TBH, I'm not sure PC floppies even use the index pulse for anything other than formatting the disk. Once the disk is formatted, it's kind of redundant information. But it's required by the spec, forcing PC floppy drives to include the sensor.

Tuna-Fish

3 months ago

The motor signal not being aligned to sectors of the disk doesn't matter because the drive doesn't care about angular position. The track header is generally not used for anything, on PC drives it's ignored and can be left out if you want to fit a few more bytes on the drive.

Unlike hard disk drives that use servo data to decide where to read and write, floppy disk drives generally don't know the angular position of either the drive or the sectors and use an extremely simple algorithm. In a very real way, they work like tape drives except they can freely choose one from a bunch of circular tapes to work on.

When ordered to read a specific sector, the drive seeks to the track requested, and then reads the track continuously until it sees the sector header magic value. Then it compares the track and sector numbers after that header with the requested numbers, and if they match, it waits for the magic value (000000000000000000A1A1A1F{AB}) and then starts reading. The magic number is designed to reinitialize the PLL, and also give the drive electronics enough time to make the comparison and decision of whether to do anything. If the numbers didn't match what was requested, then it just keeps reading until it has received a defined amount of pulses from the motor, usually 2 or 3, at which point it returns an error.

The sectors don't have any defined order on the track. You can do weird things like order your sectors linearly except have one specific one out of order, have multiple sectors with the same sector number on the same track (in which case which is returned on read depends on which you happen to hit first), have a sector with the wrong track id on a track (that gets ignored by normal read/write commands, but can be accessed with low-level ones), index your sectors with a set of random numbers between 1 and 255 instead of sticking to 1-18, and plenty more. All these have been used in various hare-brained copy protection schemes. The drive electronics are too simple to care, they just compare one number with another and do a single decision based on it.

teddyh

3 months ago

From what I heard, the index hole was not used except by extremely old systems; i.e. IBM PCs never used them.

proactivesvcs

3 months ago

At 1,685,278 bytes this almost fits on within the hallowed 1.44 megabytes. Maybe the front and rear covers can be discarded?

Tuna-Fish

3 months ago

A storage disk doesn't need ability to do random block writes, if you ditch that you can remove the sector gaps and put more sectors on the drive. The Microsoft DMF format and utility can put 1,720,320 bytes on a drive.

iberator

3 months ago

Linux can do this as well.

manwithaplan

3 months ago

It should fit on an DMF MF-2HD (standard double-sided, high density, 90 millimeters microfloppy formatted in Distribution Media Format, holding 1'720'320 bytes).