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Can you format each individual side of a double sided disk?
- Thread starter olePigeon
- Start date
Could a flippable 3.5 inch disk be created? The current 3.5 inch disk is asymmetric. If it could be made symmetric, would it still work?
Is the plane of the floppy centered between the top and bottom of the floppy shell? If not, then flipping can't work.
First thing to change is the sliding metal protection. If you remove that, can the disk still work?
Next thing to change is the rotating middle. Both sides would need to be open and have that metal circle with holes.
Third thing to change is the angled corner. If both sides were angled, would a floppy drive accept it?
Basically, the top of the floppy would need to be replaced with a bottom (since the bottom has all the features).
If you can't flip the 3.5 inch disk upside down then:
Can a floppy have a partition map? Standard macOS formatting tools won't do it but what if you create a disk image with a partition map and block copy it onto the floppy? With a partition map containing two partitions, each partition would includes parts on both sides of the floppy. You can't have each partition be written on a single side. If you want to do that, then you would need to make a different floppy driver.
Is the plane of the floppy centered between the top and bottom of the floppy shell? If not, then flipping can't work.
First thing to change is the sliding metal protection. If you remove that, can the disk still work?
Next thing to change is the rotating middle. Both sides would need to be open and have that metal circle with holes.
Third thing to change is the angled corner. If both sides were angled, would a floppy drive accept it?
Basically, the top of the floppy would need to be replaced with a bottom (since the bottom has all the features).
If you can't flip the 3.5 inch disk upside down then:
Can a floppy have a partition map? Standard macOS formatting tools won't do it but what if you create a disk image with a partition map and block copy it onto the floppy? With a partition map containing two partitions, each partition would includes parts on both sides of the floppy. You can't have each partition be written on a single side. If you want to do that, then you would need to make a different floppy driver.
@joevt I do know they can be formatted in cleaver ways. There are floppy disks that are formatted for Amiga / C64 / Atari. They have a single area where the respective files are stored, then there's some fancy ways they write the tracks, headers, etc. so that the disk appears to be one format or the other.
The drives literally have two different heads, one for each side of the floppy disk. So I don't see why you'd need to flip them. I was thinking that someone could talk to the drive in some low-level way, then use the top head to format one side of the disk, and the bottom head to format the other.
Just shower thoughts.
The drives literally have two different heads, one for each side of the floppy disk. So I don't see why you'd need to flip them. I was thinking that someone could talk to the drive in some low-level way, then use the top head to format one side of the disk, and the bottom head to format the other.
Just shower thoughts.
As a side note: I think it'd be fun as a general hobby to invent your own media. 3D print your own floppy disk and drive. Like some alternate universe. A flippy 3.5" disk and drive would be fun. It would also make some sense given the original 400K single sided disks and the way that the original Macintosh worked. It was intended to be like an Apple ][ where both the DOS and the program were on the floppy, and you booted directly from the floppy. So the logical progression would have been flippy disks like the original 5.25" disks and drives. 
The 3 inch diskettes used in Amstrad computers could be flipped to use both sides on the early drives for this format!
I was addressing the problem in two different ways:
A) modify only the hardware - make a flippable disk.
B) modify only the software - do weird formatting stuff.
Why would someone want a flippable disk? I can only think of this as a way to double the number of 400K floppies.
I don't recall if it was that disk specifically, but the Famicom on Japan used a similar one that they modified.
That's what I was thinking. As I said, in an alternate universe, I could've seen the original Sony 400K becoming flippable to save money on having an extra head for double sided disks. It wouldn't surprise me one bit if some of the prototypes were flippable.
I was also thinking about option B; if you could do some low-level control shenanigans and use the second head to format the backside of the floppy separately from the front side.
I wonder what would happen if you erased an 800K floppy as 400K single sided, then physically flipped the platter inside the disk, and formatted the other side. Would need to separate the hub from the disk as well, flip it, and reattach it with some glue.
I think the disk would probably work as expected on a 400K drive, but not behave any differently on an 800K drive. I think the disk header would tell the drive it's a single sided 400K and ignore the other side, even if it's formatted.
I think the disk would probably work as expected on a 400K drive, but not behave any differently on an 800K drive. I think the disk header would tell the drive it's a single sided 400K and ignore the other side, even if it's formatted.
Good luck with your experiments. New 720K floppy disks are becoming difficult to find and currently sell for twice the price of 1.4 MB floppy disks according to https://www.floppydisk.com/
A 720K floppy is not a single sided 1.44 MB floppy.
A 720K floppy is a double sided disk just like 800K floppies. It has less sectors because it's formatted using CAV instead of CLV.
360K, 400K, 720K, 800K disks are DD (double density).
1.44 MB is HD (high density).
Then I don't understand why you mentioned 720K floppy disks. You said they were scarce. I though you were thinking we could make more by using 1.44 MB disks. I think there are instructions on how to use 1.44MB disks as 720K disks (just cover one of the holes of the floppy) so you don't need to do any fancy formatting for that.
Maybe you were actually trying to say that the experiments would be expensive because the 720K disks are difficult to find and are expensive. In that case, 1.44 MB disks could be used.
But there might be an issue with DD drives using HD disks. https://www.vogons.org/viewtopic.php?p=480271#p480271
It did as I predicted. I'm guessing the disk header tells the drive to just ignore the other head when it thinks it's a single sided. Whichever platter is face up, that's the side it reads. So this would require some low level floppy hacking to make a double-formatted disk. Or design a 3.5" flippy disk.
Anyway, it was a fun experiment.
I'm guessing the disk header tells the drive to just ignore the other head when it thinks it's a single sided. Whichever platter is face up, that's the side it reads. So this would require some low level floppy hacking to make a double-formatted disk. Or design a 3.5" flippy disk.Anyway, it was a fun experiment.
Then it's that way.
I don't know which head is the default one for which side. It's whichever head reads side one (whichever side that is).I could try again.
As a historical note, on the BBC Micro you could format both sides of a double sided 5.25" double sided drive as, essentially, two separate discs, and those two sides would show up in two "drives", one of which corresponded to the top head, one to the bottom head.
This got superseded because it wasn't actually that useful compared to, you know, working directories and stuff.
So, in theory there's no reason why it couldn't be done, but the software for floppy filing systems tend not to, because there are generally far better ways of solving any of the actual problems that it would address.
This got superseded because it wasn't actually that useful compared to, you know, working directories and stuff.
So, in theory there's no reason why it couldn't be done, but the software for floppy filing systems tend not to, because there are generally far better ways of solving any of the actual problems that it would address.
