Everything I know about floppy disks
thejpster.org.uk
thejpster.org.uk
The operator I knew frequently had this folded up in his pocket: You just had to smooth it out a bit, make sure it rotated inside its kevlar sleeve, and off you went.
(DECTAPE was famously robust, everything was written out about 5 times in the tape, it was designed for light industrial deployments. It was wide like old school 16 track audio tape, not like classic 1/2" 800/1200/9600 bpi computer tapes, before DAT/DLT cartridges and the like. But that said, the old tapes were pretty robust too)
That’s exaggerated, but the first 8” floppy held only about 80 kilobytes (https://www.ibm.com/ibm/history/ibm100/us/en/icons/floppy/br...), with tracks that were over half a mm wide (32 tracks/inch), and about 62 bits/mm. It also was read-only.
Reading https://archive.org/details/ibmrd2505ZE/page/n5/mode/1up, that soon become about 250kB. That’s also what DEC’s first ones stored, according to https://en.wikipedia.org/wiki/List_of_floppy_disk_formats.
Early drives only wrote on one side of the diskettes. Someone discovered that diskettes had magnetic material on both side, so the diskette could be flipped and written on, doubling the storage. A notch would have to be cut to make it read/write, but it worked relatively reliably.
Later drives got second read/write heads and the flipping went away.
On the 3 1/2" diskettes this became a sliding tab. But, in their wisdom they flipped the concept. They reversed it. "missing" or open notch meant write-protect, and closed notch meant read/write.
For example the write/read-head in a C64 floppy was placed on the bottom, so the down side of the floppy got magnetized. But the head of the floppy drive from a Atari 800 was placed at the top, so the upper side got magnetized.
So basically, when a floppy was sold as 1S (single sided) this was pure marketing. :) At least for the most floppy drives.
There's also a second thing, the "index hole". On real 2S floppy there are 2, one for each side. But most of the drives didn't care about this index hole. So, this wasn't relevant for C64 users and such.
Before the data of each floppy sector, is a sector header. Among other information, it contains a flag byte, which can have two different values, indicating two different types of sectors – normal and deleted. There are different commands to read/write normal sectors vs deleted sectors. Historically, this came from the IBM 3740 data entry system, where each (128 byte) floppy disk sector stored one database record, there was not much in the way of a filesystem, and you would delete database records by changing a normal sector into a deleted one. Subsequent systems (such as IBM PC floppy controllers) retained this feature despite it being useless for their purposes. Almost no microcomputer/PC software ever used it, the principal exception being that it saw repeated (ab)use to implement an (easily circumventable) form of copy protection. Apparently, some late model PC floppy controllers (1990s / early 2000s, just before floppy drives disappeared entirely) dropped support for deleted sectors completely, viewing it as a disused legacy feature which was a waste of circuitry to support.
Well, that's true for any floppy based on the traditional IBM minicomputer/mainframe floppy format, which includes IBM PCs and many CP/M systems. It isn't true for floppy disk formats which lack that IBM heritage, for example Apple II floppies.
https://en.wikipedia.org/wiki/Count_key_data
There were no sectors, just data fields. Also each data field had a text key field. I think IBM only gave this up (really virtualized it) when commodity hardware became better than their own.
So I'm wondering if CKD was ever a thing on floppies?
That's not really true – an (E)CKD record is fundamentally the same thing as a sector. The difference is that on standard hard disks (what in IBM nomenclature is called FBA DASD), the norm is every sector on the disk has the same size; CKD permits each track to have a different sector size, and even different sized sectors on the same track. Also, CKD optionally has separate key and data fields, with a physical gap between them; in floppies and standard hard disks, there is only count and data fields (count = sector header), and any key-data separation has to be marked logically (by a byte offset) not physically.
> So I'm wondering if CKD was ever a thing on floppies?
No, CKD was never used for floppies. In the standard IBM floppy format, the sector size is in the header of each sector, so in principle you could have a mix of different sized sectors on the same track, like CKD permits; in practice, I've never heard of anyone doing that, I question whether the floppy disk controller could cope with it; even if the FDC somehow could, almost all software would be confused by it. (I suppose if the FDC can handle it, someone may have adopted it as part of a floppy disk copy protection scheme.)
Something which did actually happen, albeit rarely, was formatting the first track on the disk as 128 byte sectors, and the remaining tracks with bigger sectors (such as 256 or 512 byte), to retain some limited backward compatibility with older systems that only supported 128 byte sectors; at least being able to read the first track might make clear it was a valid disk that just couldn't be read on this system, as opposed to thinking it was an invalid disk, and then formatting it in response, causing the loss of that valid data. Systems that did this sometimes also physically recorded that first track as FM, while using MFM for the remaining tracks. This was largely a 1970s concern; by the time the 1980s came around, systems which only supported 128 byte sectors had become practically irrelevant.
The classic IBM 3740 floppy filesystem supports record-oriented files. Some vendors other than IBM adopted it (e.g. Olivetti), but most non-IBM vendors ignored it, and developed their own filesystems instead (e.g. the CP/M filesystem, Microsoft's FAT). ECMA standardised an ASCII version of it as ECMA-91 in 1984 [0]. That standard didn't support keyed/indexed files, but could easily have been extended to support it–if anybody had cared to do so, as I said, relatively few vendors ever paid attention to it. The 3740 did support a key field in each database record (sector), but the key-data separation was only marked logically (by a byte offset into the data), not physically by a recording gap.
[0] https://www.ecma-international.org/wp-content/uploads/ECMA-9...
That was actually done by IBM to distribute some versions of OS/2 2.x (or was it a later one?). It was called XDF and was originally invented by a company making backup-to-floppy software. And of course it needed a special driver to access: IIRC the one built into OS/2 was also read-only, and the first few installation floppies were in standard format so that you could boot from them.
The PC floppy controller itself has no problem reading or writing different-sized sectors, provided you didn't try to do multiple ones in a single command.
But creating the low-level format with PC hardware required a crazy hack: fill the track with 128-byte sectors without any gap between, but setting up the "C,H,R,N" header fields for larger sectors with the correct spacing. The remaining dummy sectors would then become part of the larger sectors' data and gap field, so their headers didn't matter (and would be overwritten when writing the actual data).
Although there is still a big difference between floppies and CKD hard disks – on IBM standard floppies, the sector size has to be a power of 2, minimum 128; on CKD hard disks, the sector size can be anything – 80 byte sectors, 300 byte sectors, whatever one wishes. On z/OS, several file formats require a 3120 byte block (=sector) size. Under CMS, the standard sector size is 800 bytes.
Hard disks (as opposed to floppies) commonly support non-power of 2 sector sizes, of 520 bytes or 528 bytes – for RAID systems which need to store additional metadata with each 512 byte sector. And with newer 4096 byte sector support, one sometimes finds support for 4104, 4160, and 4224 byte sectors. But, that's still not like CKD, in that most hard disks only support a fixed set of sector sizes (512 or 4096 base size plus some bytes of per-sector metadata), not arbitrary sector sizes like CKD does.
However, it seems you might actually be right in practice. I think early 3.5" definitely did this, but while googling to determine what orientation of the hole triggers the index pulse came up with nothing, except a few patents about how you can fake an index pulse by using a timer and a speed sensor instead.
So maybe because almost nothing was actually using the index pulse anymore when 3.5" drives were introduced because almost every modern system (for the time) had settled on soft-sectoring, it's entirely possible that I've always been mistaken and there's never been a standardised index pulse for 3.5" drives between different drives relative to the "start of the track".
I guess this might explain why even though the Amiga allowed you to read the INDEX signal, it actually didn't use it and instead read a whole track at once starting when it saw a particular sync word.
Our school's collection of BBCs included one drive that could read everything, including data it had created, but most of the other drives would reject anything it had written. Once identified that drive was taken out of general circulation and only used to read data for writing to a new disk in a second drive, and eventually skipped once it was unlikely any data someone cared about had been written by it and not copied elsewhere.
This often comes down to regularly testing old data. Floppies shouldn't have been used for archive storage but often were, with a problem only being noticed years down the line when the data needed to be read. Other media similarly: recorded CDs and DVDs from a decade or more ago are sometimes not readable now. An archive is only an archive if you can actually read it, much like an untested backup is just a hope not really a backup.
It was a different time...
Students adapt to the times...
> The Victor 9000 was perhaps best known for how it was able to achieve such high density on it's floppy disks. It used variable speed disk drives; there were 9 different speeds used. As the drive head moved outward the speed would increase. It was really neat to hear the speed change as the drive head moved.
https://www.old-computers.com/museum/computer.asp?st=1&c=210
A thumb drive is much better, as long as it not one of those thumb drives that's barely bigger than a USB port. But for offline storage that can be easily filed into a cabinet and paged through, floppy disks really were a great size. You can't file thumb drives; they're too narrow and thick, so a collection of them just ends up being a pile.
It's really too bad we don't have some kind of inexpensive, high-reliability, high-density offline storage format that resembles 3.5" floppies.
I know modern devices don't have a lot of space, but regular SD cards and mini-SIMs weren't really that big. (The full credit card sized original SIM card size is dramatically oversized though)
This is true, but the idea is that you should almost never need to do this. It should be a rare occasion when you need to install or remove a microSD card. It's just like nanoSIM cards: when was the last time you needed to swap that out?
Floppy disks, and today USB thumb drives, serve a different purpose: they're supposed to be easy to plug and unplug and move data around. I don't see microSD cards as having that purpose at all. I have a microSD card in my phone, and it's great, but I haven't taken it out since I put it in there several years ago; it's just a storage expansion device, not a way of easily moving data between devices. It's not that easy to swap between devices, but it's easy enough to do, with some care, for those rare occasions it might be necessary (like migrating to a new phone).
You'd really think that Sony would have figured out that every single storage medium they've ever made has been an utter failure, but Sony is gonna Sony.
Also Sony: No, not like that.
Sony's positioning in storage formats is just weird. They spend untold money developing media formats intending to recoup the development costs licensing those formats. Then make the licensing fees and conditions so onerous that no one is willing to license them. The only time anyone touches a Sony influenced format is when it's developed and licensed by a consortium.
Case in point: Vita Memory Card. Superficially similar to Micro SD, and it even uses a similar electrical protocol... but it isn't compatible.
It reminds me a lot of IBM when they introduced the PS/2 computers. They really, really thought that they could single-handedly kill all the PC "clones" by pushing their clunky, overpriced PC with a bunch of proprietary standards in it (namely the MCA bus). The people running these two companies had an extreme amount of arrogance and hubris.
This is a little funny in a thread about floppy disks, considering that the extremely popular and ubiquitous 3.5” Micro Floppy Disk was a Sony design ;)
There are also some other Sony formats that actually stuck, like DAT, Minidisc (yes, not so much in the US from what I gather, but it was A Thing in Europe, Australia and Japan) and Betacam.
These cards are much sturdier than the SD cards, and much faster, due to the PCIe interface. If a laptop had a slot for them, they would have been much more convenient than external SSDs or USB drives, which protrude from the case or are hanging on cables.
https://retrocmp.de/ is also a great reference for particular drives. And if you need floppies, email Tom at https://www.floppydisk.com/ - he’s a top bloke and the disks I’ve got from him have all been in great working order.
Another related article to this: http://www.trevormarshall.com/byte_articles/byte19.htm
Title: “How did Microsoft store 1.68 MB on Windows 95 Setup diskettes?”
The Floppy Disk Museum on a Bootable Floppy serving from a 286 PC
However, it's literally impossible to find USB to 5 1/4" floppy interfaces now in Europe. I only found one outfit in the US that sells them, but they refused to ship to europe :(
If anyone has any tips I'd appreciate it because I'm pretty lost now.. I have much old hardware but nothing that can drive a 5 1/4" floppy drive. It's mostly unixy stuff like HP9000's and Macs.
Not shipping outside the US is routine so there's many services out there catering to that.
But I'll use this greaseweazle, it sounds good!
[edit] This might be your ticket: https://github.com/keirf/greaseweazle/wiki (Someone just posted this in another comment)
EDIT: actually, no, I just looked it up — the Z400 will take a 1.2MB 5.25” drive. It will not take DD drives of any kind.
Along with a cool article by the inventor about how it works:
Adult me is now going to go look into how or why that worked.
Why do I think it's biological -- just the shapes of the patches resemble what you see in laboratory petri dishes, and that the amount of such corruption seems to correlate to humidity. Disks from an attic seldom have this issue, compared to ones from basements.
It also means if you drop it in water (as I once did) the felt will expand then be dragged along with the disk and literally crash into the head if you were foolish enough to put it in a drive. (Which I fortunately didn't.) Drying it out is not simple. But for the 3.5" types opening the shell is. You can then transfer the disk into a donor shell after giving it a good wipe with lint-free cloth and be on your way.
For dealing with mold on the disk itself, a brief Duck search reminds me that UV light kills most biologics. As does ozone. That will at least stop it from growing.