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I think that I have once seen an Internet article, which stated, that special drives are capable of making many megabytes of data out of one ordinary MF-2HD floppy disk. But I am unable to find it again.

Did such a drive actually exist?

Is there any more accurate documentation about this technology? Is there any way to store 32MB on a MF-2HD in 2018? And what aboue DD and ED disks?


I found more information here:**

Wikipedia article mentions Zone Bit Recording.

Because the sectors have constant angular size, the 512 bytes in each sector are compressed more near the disk's center. A more space-efficient technique would be to increase the number of sectors per track toward the outer edge of the disk, from 18 to 30 for instance, thereby keeping nearly constant the amount of physical disk space used for storing each sector; an example is zone bit recording.

Is that high density writing technology with 32MB still CAV or CLV like optical discs (CD, DVD, HD-DVD, BD, etc.)? Does it utilize ZBR?


Answer on other question by @ChenMunka:

http://retrocomputing.stackexchange.com/a/5449/7641

You would not expect a quick format to repair corruption from magnetic fields as it doesn't recreate the track and sector sync markers.

This means, that the track sector information can be written on a format. Does that not mean, that an ordinary drive could possibly squish like 10MB on a floppy disk by formatting it with different track/sector information?

to format or write to this high-coercivity media, the high-density drive switched its heads into a mode using a stronger magnetic field. When these stronger fields were written onto a double-density disk (having lower coercivity media), the strongly magnetized oxide particles would begin to affect the magnetic charge of adjacent particles. The net effect is that the disk would begin to erase itself.

How long does it take for the floppy disk to erase itself when treated like an ED? Can I store 2.88MB on MF-2HD for 10 minutes?

  • There are so many possible ways of interpreting this question that I'm not sure it can be objectively answered. – wizzwizz4 Jan 14 '18 at 14:40
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    What is not specific? – neverMind9 Jan 14 '18 at 16:59
  • @Chenmunka Invitation to discussion. – neverMind9 Jan 15 '18 at 11:17
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    This question seems to be about actual products that really existed, but a quick back-of-an-envelope calculation suggests to me that if you had a constant linear velocity (rather than angular) you'd fit about 2.2 times as much data. Switch from MFM to (2, 7) RLL for an extra 50% and assume the controller uses a variable clock to give a constant linear velocity for data while spinning at a constant angular velocity and you're at 3.3 times as much data without even having to modify the drive. Which is around 6.5mb unformatted. Improve the drive and you could definitely do better. – Tommy Jan 17 '18 at 20:38
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Note that beyond SD, DD, and HD formats for 3.5" disks there was ED (extra density) with double the capacity of a HD disk (2.88 MBytes formatted, 3.5MBytes raw capacity and double the data transfer rate of a HD disk). Disks and drives looked the same but were much less common than HD technology. You had to use specific ED-Disks to use the higher capacity in those drives, the drives could, however, read and write HD and older disks.

As that was pretty late in the development of floppy disk technology, only a few vendors picked that up (IBM PS/2 and the NeXT computers are some of the more prominent examples, I happen to have a twin ED disk set for a Sinclair QL that gives me ~5MB of storage, the size of a small hard drive.

Today, drives (and, especially, disks) supporting the ED format are relatively hard to come by and expensive because of their rarity.

ED was the last open industry standard supporting the highest capacity for 3.5" floppy technology.

Beyond the official standards (and some years later) was the Superdisk mentioned by dirkt already with much higher capacity that could also read and write 1.44M disks, but these were combi drives - You could use "normal" 1.44M floppies in these drives, but only with their limited capacity. To my knowledge, Superdisk drives could not work with ED media. In order to use the up-to-120M capacity the drives had, you had to use specific Superdisk media that could use their magneto-optical technology and looked a bit different from standard 3.5" floppies.

Later Superdisks could, apparently, with some special software supplied by the vendor, write up to 32M to a standard 1.44M floppy. The drive, however, lost its random access capabilities with that usage and basically degenerated to some sort of tape drive. It also didn't show up as a block device to the computer and could only be used in that way through the vendor application.

I guess Superdisks (both media and drives) are even harder to come by today than ED. Superdisks were replaced relatively fast by the upcoming CD R/W pure optical drives.

There were other proprietary Superdisk-like technologies from Iomega and Sony that more-or-less worked similarily (optical laser-based positioning and magnetic data storage).

Superdisks and similar devices are, however, in my opinion at least borderline off-topic for this site, as they are 3rd-millennium technology.

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    Also there was the 2.88MB format. – snips-n-snails Jan 15 '18 at 3:08
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    @traal Erm, that's described in half of the answer as ED format? – tofro Jan 15 '18 at 7:54
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    Is there any more information about this 32MB MF-2HD floppy disk? Can it be reproduced on other drives by firmware hacking? How exactly does it work? Is it documented somewhere? How can this be done today? – neverMind9 Jan 15 '18 at 8:07
  • @TechLord You might have some luck when searching for Packet Drive and I doubt you could reproduce that on a standard drive. The Superdisk must use a much higher data transfer rate, i.e a controller that is much higher clocked than a standard FDC to achieve that capacity. – tofro Jan 15 '18 at 8:24
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    @tofro I suspected that but I never saw them marketed as "ED" or as 2280kB disks, only as 2.88MB disks. – snips-n-snails Jan 15 '18 at 17:25
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The Wikipedia table of floppy disk formats has five entries at the bottom with capacities of hundreds of MB, namely the Superdisk (LS-120 and LS-204), the UHD144, and the Sony HiFD (HiFD 150 and HiFD 200).

These all seem to be flopitcal technology, where a laser or similar is used to position a "normal" read-write-head.

They all seem to have been able to read ordinary 1.44MB floppy disks or similar standard formats, but I couldn't find any information if the higher densities required different floppy disks (because the magnetic material might have needed different characteristics), or would also work with HD-type floppy disks.

  • IIRC I think my oscilloscope got one LS-120 (at least that is how BIOS recognize it) drive but I never used it differently then to boot a MS-DOS from 1.44MB floppy (so the backward compatibility with 3.5" HD is still there). The drive itself is build in but looks exactly like a standard FDD from the outside. – Spektre Jan 14 '18 at 20:30
  • @Spektre: So then the obvious thing to try is to format a normal 3.5" HD with the 120 MB, and see how it goes ... But I've found indications that special media were needed, so it probably won't work. – dirkt Jan 14 '18 at 20:38
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    Floptical drives needed special media to use the higher capacity: "while optically aligning the read/write head in the drive using grooves in the disk being sensed by an infrared LED" (Wikipedia). No such grooves exist on a standard floppy disk, and it is unlikely that magnetic domains themselves were read and aligned to optically - this would likely have been uneconomically complex technology at that time. – rackandboneman Jan 15 '18 at 9:58
  • One nice thing about certain LS-120 drives was they could read normal 1.44MB floppies at 2x and 4x speeds. – Ross Ridge Jan 15 '18 at 23:15
  • These formats use media that is radically different from "an HD floppy disk", even if comes in a compatible package... – rackandboneman Oct 17 '18 at 11:47
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For what it's worth: In the late 80s to early 90s, I remember writing a DOS floppy driver (a TSR) that allowed formatting a few more tracks/sectors on a 3.5" drive in order to boost the capacity of the 3.5" floppy drives past 1.44MB. I kept it to myself and it was not released to the public (though it was shared with some coworkers at Epyx Games). If my (fuzzy) memory is accurate, my boosted capacity was still under 2MB, and was rather sensitive as to the quality of the media. I believe I also encountered issues with certain BIOS / drives doing error checking of the read/write parameters (or just not being able to physically move where requested) and vomiting with "too big" numbers. One advantage of working at Epyx Games is there were a wide variety of drives and systems to play with ( "test on") because much of the game testing was done in-house.

A variation of this notion was used for one of Epyx's copy protection schemes on a few different platforms. A game's floppy disk sector was marked for the BIOS as 'bad', but contained key data that the game looked for. Normal disk duplication would only read/write the good sectors, resulting in what appeared to the user (and many disk copy programs) to be identical disks that behaved differently. The game was able to use low-level coding to read the 'bad' sector (as raw data) to determine if the disk was an original or not.

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