Hey all. So I've heard that some DD (360kb) floppy drives won't read DD disks if they were formatted in a HD (1.2mb) floppy drive (using the /f:360 option)

For the past year or so I've been selling bootable floppy disks on ebay (360kb, 720kb, 1.2mb and 1.44mb) and have checked with the people who bought 360kb disks to make sure they worked correctly. So far they have. I also have a coworker with a compaq luggable computer with 360kb floppy drives and made him boot disks which he says works fine.

A few weeks ago I picked up a 360kb drive but it has a strange quirk that disks formatted and made bootable in that drive will only boot in that drive.
This DD drive will also boot fine off of a DD disk formatted in an HD drive.

My question is has anyone actually experienced a situation where DD disks formatted in a HD drive will not boot and/or read in their DD drive? If so can you let me know what type of drive it is (manufacturer/model #) or at least what computer it is in?

I'm trying to work out if this is actually a problem and if so for what drives

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My question is has anyone actually experienced a situation where DD disks >formatted in a HD drive will not boot and/or read in their DD drive? If so can
you let me know what type of drive it is (manufacturer/model #) or at least >what computer it is in?

I think it might be an issue if someone did not use the correct switches, possibly in an effort to get more than 360 out of them. There were also software packages back in the day which would allow you to format a 360
disk as > 360, even in a 360 drive. I did that on my old XT machine. When
I later got a 386 with a HD drive, it would read them without the special driver being installed, but other 360 drives would not.


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On 01-22-20 07:23, Divarin wrote to All <=-

@VIA: VERT/MUTINY
Hey all. So I've heard that some DD (360kb) floppy drives won't read DD disks if they were formatted in a HD (1.2mb) floppy drive (using the /f:360 option)

This is true. The reason is because of the different widths of the tracks created by DD and HD drives. DD drived have 40 tracks, HD drives cram 80 tracks into the same space. If the disk has been used before, the residual information from the underlying DD track appears as "noise" to DD drives.

For the past year or so I've been selling bootable floppy disks on ebay (360kb, 720kb, 1.2mb and 1.44mb) and have checked with the people who bought 360kb disks to make sure they worked correctly. So far they
have. I also have a coworker with a compaq luggable computer with
360kb floppy drives and made him boot disks which he says works fine.

Geerally if the disk is formatted and written to with a DD drive, it should be fine.

A few weeks ago I picked up a 360kb drive but it has a strange quirk
that disks formatted and made bootable in that drive will only boot in that drive. This DD drive will also boot fine off of a DD disk
formatted in an HD drive.

Hmm, sounds like a head alignment issue.

My question is has anyone actually experienced a situation where DD
disks formatted in a HD drive will not boot and/or read in their DD
drive? If so can you let me know what type of drive it is (manufacturer/model #) or at least what computer it is in?

Yes, this was a very common issue. Not just formatted, but if written to by a HD drive at any stage.

I'm trying to work out if this is actually a problem and if so for what drives

It was pretty brand independent, from memory. I was studying at university at this time and frequently encountered this issue. Only way to avoid it was to ensure that DD disks were either written to only by a DD drive, or only used in a HD drive. Some PCs had a HD and a DD drive, which made it easy to copy disks and avoid the issue, or to use the DD drive for all writing operations.

Later, the transition to 3.5" floppies solved the problem altogether, because 4.5" disks don't have this issue (DD and HD both have 80 tracks, but a different number of sectors per track).



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Re: Re: 360kb floppy disks
By: Vk3jed to Divarin on Thu Jan 23 2020 11:46:00

A few weeks ago I picked up a 360kb drive but it has a strange
quirk that disks formatted and made bootable in that drive will
only boot in that drive. This DD drive will also boot fine off
of a DD disk formatted in an HD drive.

Hmm, sounds like a head alignment issue.

my thoughts exactly... i remember aligning full height drives with special disks back in the day... not only aligning the heads via ocilliscope on the x and y axes but also adjusting the trim pot for the speed...

i forget if the x axis was from the center to the edge (track alignment) or if it was for the angle from the center to the edge (track twist alignment)... ideally, the head should be square over the track without any twist meaning 90 degrees from the center out... if there was any twist, then only a portion of the head would be in the proper place to read/write the data... if there was any twist, reading could read data from parallel tracks and writing would write a wider track than desired...

it was fun stuff for sure ;)


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Re: Re: 360kb floppy disks
By: Vk3jed to Divarin on Thu Jan 23 2020 11:46:00

This is true. The reason is because of the different widths of the tracks information from the underlying DD track appears as "noise" to DD drives.

Hmm it sounds like all of the DD floppies I've formatted in the HD drive should only work in HD drives then but, at least so far, they're working in DD drives.

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Re: Re: 360kb floppy disks
By: Vk3jed to Divarin on Thu Jan 23 2020 11:46:00

Hmm, sounds like a head alignment issue.

I don't know the disks seem to read and write just fine otherwise. I tried surface scans and I tried reading the disk created in this drive in the HD drive and in all cases the disk seems to read and write without issue and without any indication if difficulty accessing the data.
Unless an alighment issue would only affect the recording of the boot record.

Any ideas how I could go about checking / fixing the alignment?

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On 01-24-20 06:27, Divarin wrote to Vk3jed <=-

@VIA: VERT/MUTINY
Re: Re: 360kb floppy disks
By: Vk3jed to Divarin on Thu Jan 23 2020 11:46:00

Hmm, sounds like a head alignment issue.

I don't know the disks seem to read and write just fine otherwise. I
tried surface scans and I tried reading the disk created in this drive
in the HD drive and in all cases the disk seems to read and write
without issue and without any indication if difficulty accessing the
data. Unless an alighment issue would only affect the recording of the boot record.

Any ideas how I could go about checking / fixing the alignment?

Yeah there's probably others in here better qualified to answer that. :)


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Divarin wrote to All <=-

Hey all. So I've heard that some DD (360kb) floppy drives won't read DD disks if they were formatted in a HD (1.2mb) floppy drive (using the /f:360 option)

Hmm... I haven't tried the 5.25" diskettes like that. The only 5.25" systems I have are the C-64 (where I've put the 1541 away and use a 1541 emulator that reads an SD card) and my newly renovated TRS-80 Model 4P.

But, remembering way back, I don't recall having a problem using HD diskettes in a DD drive and vice versa.

I do know that is NOT the case for 3.5" diskettes. If you use a 3.5" HD diskette in a DD drive, you will get high failure rates. I found that out recently with my Tandy 1100FD and had to locate some DD floppys.


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