DustyShinigami wrote on 2025-11-15, 17:27:

So what you're saying is, ImageDisk will format it in such a way that it can have images written to it, but Windows won't recognise it ...

It's important to understand that what most people think of as "formatting" is actually two distinct functions:

1) Low level format
This create tracks containing blank sectors - depending on the disk there are different numbers of side, tracks and sectors/track.
This operation is necessary as it provides the base (lowest level) of disk organization, and places each specific sector (a block of data) at known and controller places on the disk.
This is how certain data can be written to the disk without affecting other data on the disk - ie: the floppy controller hardware can write
specific blocks of data by: Side, Track and Sector#

2) After 1) the OS performs a "higher level format" - which means writing certain sectors with the various data blocks the OS needs to keep track of it's disk organization.
In the case of DOS, this would be writing boot sectors, file allocation tables and root directory all at certain known places on the disk. The OS will read/modify and expand on these as it add/removes "files" from the disk (A file is just a collection of data sectors, pointed to by the directory, and linked/expander/contracted by entries in the file allocation table.

Other OSs organize their higher level disk/file structure differently - which is why for example, DOS couldn't read Winblows NTFS volumes (there were special add-ons to enable partial ability),
Dos/Winblows, UNIX, VMS, MVS, and *lots* of different OSs can't read each others disks.

All OS's do however have to build their unique disk structure on a low-level formatted disk!

ImageDisk does the low-level format, but as it works with images which could be *any* OS (even ones I've never heard of), it does not do any sort of high level format.
(You can read a new formatted/blank disk from any OS with ImageDisk and later write it back to a different disk, effectively formatting that disk for the OS that created th original)

- And ImageDisk can low-level format each track before it writes that track from the image, effectively making it appear as a "one step" process (like most OSs do)

ImageDisk doesn't know about the high-level format at all, it's just replicating a black formatted disk made by an OS.

The ability to low-level format a disk in ImageDisk isn't something most users ever need - but I did originally write ImageDisk for my own use, and sometimes I find it useful to low-level format a disk without having to rely on an os and whatever "junk" it writes as part of it's format process.

DustyShinigami wrote on 2025-11-15, 17:27:

... I'm not sure if a tape eraser was ever released in the UK...? ...

I'd be surprised if they weren't - they were quite common in the days of extensive audio recording on actual magnetic tape.

They look like a small box (containing the electromagnet) with a handle on it to easily hold/pass is over media.
Picture a small rectangular Kettle ...

I still have a couple - turns out these were for Video tapes, I do recall them being available for reel-to-reel audio tapes (functionally identical, the only difference is the label)

DaveDDS wrote on 2025-11-16, 02:27:

It's important to understand that what most people think of as "formatting" is actually two distinct functions: […]
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DustyShinigami wrote on 2025-11-15, 17:27:

So what you're saying is, ImageDisk will format it in such a way that it can have images written to it, but Windows won't recognise it ...

It's important to understand that what most people think of as "formatting" is actually two distinct functions:

1) Low level format
This create tracks containing blank sectors - depending on the disk there are different numbers of side, tracks and sectors/track.
This operation is necessary as it provides the base (lowest level) of disk organization, and places each specific sector (a block of data) at known and controller places on the disk.
This is how certain data can be written to the disk without affecting other data on the disk - ie: the floppy controller hardware can write
specific blocks of data by: Side, Track and Sector#

2) After 1) the OS performs a "higher level format" - which means writing certain sectors with the various data blocks the OS needs to keep track of it's disk organization.
In the case of DOS, this would be writing boot sectors, file allocation tables and root directory all at certain known places on the disk. The OS will read/modify and expand on these as it add/removes "files" from the disk (A file is just a collection of data sectors, pointed to by the directory, and linked/expander/contracted by entries in the file allocation table.

Other OSs organize their higher level disk/file structure differently - which is why for example, DOS couldn't read Winblows NTFS volumes (there were special add-ons to enable partial ability),
Dos/Winblows, UNIX, VMS, MVS, and *lots* of different OSs can't read each others disks.

All OS's do however have to build their unique disk structure on a low-level formatted disk!

ImageDisk does the low-level format, but as it works with images which could be *any* OS (even ones I've never heard of), it does not do any sort of high level format.
(You can read a new formatted/blank disk from any OS with ImageDisk and later write it back to a different disk, effectively formatting that disk for the OS that created th original)

- And ImageDisk can low-level format each track before it writes that track from the image, effectively making it appear as a "one step" process (like most OSs do)

ImageDisk doesn't know about the high-level format at all, it's just replicating a black formatted disk made by an OS.

The ability to low-level format a disk in ImageDisk isn't something most users ever need - but I did originally write ImageDisk for my own use, and sometimes I find it useful to low-level format a disk without having to rely on an os and whatever "junk" it writes as part of it's format process.

Wow. Thanks for the lengthy explanation. That's a lot of info to process; I'll probably need to re-read it a few times, but I think I get the general gist. 😀

Also, how exactly do magnets help some disks fix their broken sectors? What does it actually do?

DaveDDS wrote on 2025-11-16, 02:33:

I'd be surprised if they weren't - they were quite common in the days of extensive audio recording on actual magnetic tape. […]
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DustyShinigami wrote on 2025-11-15, 17:27:

... I'm not sure if a tape eraser was ever released in the UK...? ...

I'd be surprised if they weren't - they were quite common in the days of extensive audio recording on actual magnetic tape.

They look like a small box (containing the electromagnet) with a handle on it to easily hold/pass is over media.
Picture a small rectangular Kettle ...

I'll try asking someone I know if they came across any.

DustyShinigami wrote on 2025-11-16, 11:25:

... Also, how exactly do magnets help some disks fix their broken sectors? What does it actually do?

A magnet just changes magnetic domains on the disk - just like the drive head does while writing.

The reason it helps sometimes is that OSs/FDCs can be stupid and if certain bits get accidentally "set" in the disk organizational information which is written in addition to user users files, the system can see a "state" that it doesn't recognize or know how to recover from. A magnet can corrupt the sectors enough that it doesn't see this state.

The problem with magnets is that they don't really "randomize" the domains like an unwritten disk - it usually works ... but it's not the same as unformatted.

Also, if bad people with a lot of money want to recover your data, the much more consistent effect of a magnet is much easier to "see under" and retrieve what portion of the original domains remain (remember that magnetic media is analog in nature - which means that a write of a domain adds/subtracts from the original - normally it is so strong that what little remains of the original is just low-level "noise" ignored by the FDC - with the right equipment someone can sometimes recover what the earlier domains were (and sector CRCs help lot is determining what recovered data is correct)

This is why I always use a bulk eraser to "fast wipe" or try and fix a disk - the result is much closed to unformatted.

DaveDDS wrote on 2025-11-16, 13:32:

A magnet just changes magnetic domains on the disk - just like the drive head does while writing. […]
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DustyShinigami wrote on 2025-11-16, 11:25:

... Also, how exactly do magnets help some disks fix their broken sectors? What does it actually do?

A magnet just changes magnetic domains on the disk - just like the drive head does while writing.

The reason it helps sometimes is that OSs/FDCs can be stupid and if certain bits get accidentally "set" in the disk organizational information which is written in addition to user users files, the system can see a "state" that it doesn't recognize or know how to recover from. A magnet can corrupt the sectors enough that it doesn't see this state.

The problem with magnets is that they don't really "randomize" the domains like an unwritten disk - it usually works ... but it's not the same as unformatted.

Also, if bad people with a lot of money want to recover your data, the much more consistent effect of a magnet is much easier to "see under" and retrieve what portion of the original domains remain (remember that magnetic media is analog in nature - which means that a write of a domain adds/subtracts from the original - normally it is so strong that what little remains of the original is just low-level "noise" ignored by the FDC - with the right equipment someone can sometimes recover what the earlier domains were (and sector CRCs help lot is determining what recovered data is correct)

This is why I always use a bulk eraser to "fast wipe" or try and fix a disk - the result is much closed to unformatted.

Hmm. Interesting. So making it unformatted is the better option? I’m still not super clear on why the domains need to be randomised and how that helps.

I take it that’s what the Erase option does in ImageDisk…?

I have been trying Flobo Floppy Bad Sector Repair, but I’m not convinced it’s doing a lot. It’s just making my system hang and there’s no indication it’s working or doing much of anything. 😕

DustyShinigami wrote on 2025-11-16, 14:08:

Hmm. Interesting. So making it unformatted is the better option? I’m still not super clear on why the domains need to be randomised and how that helps.

In almost all cases it doesn't matter - but in some very specific cases it can ... one is the case of someone trying to recover data as described above.

But another (more common) one is that few people want to take the time to move a magnet back and forth over the disk close enough to have a "super strong" effect and long enough to really overrule strong existing domains, which can come from some types of magnetic damage can be very strong - in this case, simple touching with a magnet may not reduce the effect from the previous magnetic domains enough to make it "background noise" and be ignored by the FDC - the eraser with it's alternating magnetic field "touches" the disk many times in one second (60 is Canada, 50 in Europe - line frequency) and does a much better job of eliminating existing domains.

I take it that’s what the Erase option does in ImageDisk…?

Unfortunately no, the PC hardware has no ability to write anything but formatted sectors.
ImageDisk tries to come as close as it can - by writing a sector longer than would fit on a track with randomized data - since the sector overflows the track, it overwrites the track/sector lead-in resulting in mostly random data on the track. - The sector lead-out still gets written, and it cannot "touch" the magnetic domains so many times like the erases --- so I still think the eraser is the best method.

-- Sorry, I know I've been giving way too much information -- but I've always been a big believer that to most effectively debug a system, you should have AS MUCH information on how that system works as you can get! -- even it it doesn't seem immediately relevent to the problem!

DaveDDS wrote on 2025-11-16, 15:23:

In almost all cases it doesn't matter - but in some very specific cases it can ... one is the case of someone trying to recover […]
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DustyShinigami wrote on 2025-11-16, 14:08:

Hmm. Interesting. So making it unformatted is the better option? I’m still not super clear on why the domains need to be randomised and how that helps.

In almost all cases it doesn't matter - but in some very specific cases it can ... one is the case of someone trying to recover data as described above.

But another (more common) one is that few people want to take the time to move a magnet back and forth over the disk close enough to have a "super strong" effect and long enough to really overrule strong existing domains, which can come from some types of magnetic damage can be very strong - in this case, simple touching with a magnet may not reduce the effect from the previous magnetic domains enough to make it "background noise" and be ignored by the FDC - the eraser with it's alternating magnetic field "touches" the disk many times in one second (60 is Canada, 50 in Europe - line frequency) and does a much better job of eliminating existing domains.

I take it that’s what the Erase option does in ImageDisk…?

Unfortunately no, the PC hardware has no ability to write anything but formatted sectors.
ImageDisk tries to come as close as it can - by writing a sector longer than would fit on a track with randomized data - since the sector overflows the track, it overwrites the track/sector lead-in resulting in mostly random data on the track. - The sector lead-out still gets written, and it cannot "touch" the magnetic domains so many times like the erases --- so I still think the eraser is the best method.

-- Sorry, I know I've been giving way too much information -- but I've always been a big believer that to most effectively debug a system, you should have AS MUCH information on how that system works as you can get! -- even it it doesn't seem immediately relevent to the problem!

No, it's fine. I'm learning new stuff all the time. And I find it interesting, providing I can get my head around it. :p

Sadly, the person I messaged doesn't appear to have used or come across those electro-magnetic tape erasers. Hopefully, the two spare HDD magnets I've ordered will be all I need to get the job done. Hopefully.

Okay, I've finally received these HDD magnets off eBay so I can try this experiment at fixing this floppy disk's bad boot sectors.

One question I have though - what's the best way of storing these magnets so they don't affect any electronics? In no way am I putting them in my drawer with all of my retro PC components and cables etc. ^^;

DustyShinigami wrote on Yesterday, 13:06:

... One question I have though - what's the best way of storing these magnets so they don't affect any electronics? In no way am I putting them in my drawer with all of my retro PC components and cables etc. ^^;

Assuming you've managed to get a bulk eraser as I described earlier... these are electromagnets - only strongly magnetic when powered.

They probably wouldn't effect disks while not powered, but as they have iron parts that could still have a bit a residual magnetism, I treat them like any other magnet... I wouldn't store them next to magnetic media, but any reasonable distance (a foot or more) should be fine.

DaveDDS wrote on Yesterday, 13:31:

DustyShinigami wrote on Yesterday, 13:06:

... One question I have though - what's the best way of storing these magnets so they don't affect any electronics? In no way am I putting them in my drawer with all of my retro PC components and cables etc. ^^;

Assuming you've managed to get a bulk eraser as I described earlier... these are electromagnets - only strongly magnetic when powered.

They probably wouldn't effect disks while not powered, but as they have iron parts that could still have a bit a residual magnetism, I treat them like any other magnet... I wouldn't store them next to magnetic media, but any reasonable distance (a foot or more) should be fine.

Oh no, these are HDD magnets. These:

I've not been able to find any of those erasers. These magnets appear to be strong; it doesn't take much for them to snap together.

I was just wondering if something like these could be stored in a container that would prevent them from messing with any electrical parts.

I might have to look at importing one of the bulk erasers from the States.

That HDD magnet has fixed some of the tracks, but Nformat still lists 9 that are bad. Track 6–9, 14-16, and 55 and 56.

Given it's shape and mounting brackets - That magnet was not deigned as a complete erase media tool - it's probably part of a motor or servo assembly of some kind... but enterprising people figure they can sell such old stuff they might find as a tool to erase media - not understanding why a permanent magnet is not ideal for that purpose (as explained earlier)

But a strong magnet can damage media and make it unreadable - useful for guys who want to sell such "eraser magnets".

I would keep that thing FAR away from any media I don't want damaged. I don't know how strong it is, but at least "other side of the room", possible "other side of the house".

If you have any capability "building stuff with wires in it", it's quite trivial to make an actual/proper disk eraser.

DustyShinigami wrote on Yesterday, 16:58:

... That HDD magnet has fixed some of the tracks, but Nformat still lists 9 that are bad. Track 6–9, 14-16, and 55 and 56.

It's entirely possible that the media is actually damaged and can't be easily repaired.

Getting (or making) a proper eraser won't be worth it unless you plan to do this kind of stuff a lot (I'm guessing and actual tape eraser will not be cheap these days)

DaveDDS wrote on Yesterday, 17:05:

DustyShinigami wrote on Yesterday, 16:58:

... That HDD magnet has fixed some of the tracks, but Nformat still lists 9 that are bad. Track 6–9, 14-16, and 55 and 56.

It's entirely possible that the media is actually damaged and can't be easily repaired.

Getting (or making) a proper eraser won't be worth it unless you plan to do this kind of stuff a lot (I'm guessing and actual tape eraser will not be cheap these days)

Hmm. I guess if that's the case then I'll need to revert to plan B, which didn't exactly work the first time. Although I did buy a box of brand new floppy disks, so hopefully I can take the disk out of one of those and put it into this one.

Yeah, as soon as I put a different disk inside it, it complains it's faulty and can't be read. 🙁

Is it not possible to take a diskette out of it's case and put it into another? Do they instantly become 'tainted' or something? That's two seemingly fine disks that have become broken just by putting them into another case.

DaveDDS wrote on Yesterday, 17:02:

Given it's shape and mounting brackets - That magnet was not deigned as a complete erase media tool - it's probably part of a mo […]
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Given it's shape and mounting brackets - That magnet was not deigned as a complete erase media tool - it's probably part of a motor or servo assembly of some kind... but enterprising people figure they can sell such old stuff they might find as a tool to erase media - not understanding why a permanent magnet is not ideal for that purpose (as explained earlier)

But a strong magnet can damage media and make it unreadable - useful for guys who want to sell such "eraser magnets".

I would keep that thing FAR away from any media I don't want damaged. I don't know how strong it is, but at least "other side of the room", possible "other side of the house".

If you have any capability "building stuff with wires in it", it's quite trivial to make an actual/proper disk eraser.

For now, they're at the other end of the room. On my bookcase to be exact.

But no, sadly, I have zero experience with building stuff. Certainly not something with wires. I don't mind shelling out for a proper disk eraser, but it might be something I'll get next month.

DustyShinigami wrote on Yesterday, 17:33:

Is it not possible to take a diskette out of it's case and put it into another? ...

I don't see why you couldn't - I've done it on 5.25" disks a few times - 3.5" seem more delicate and would be easier to damage.

Also, make sure you use the same case type as the original - there's an extra hole in 3.5" HD media that's not in DD media - that's how the FDC knows what
date rates it should try.