High density

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LoadError
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High density

Post by LoadError »

I bought a ZoomFloppy and recorded a batch of disks on my Oceanic OC-118 drive, with my VIC-20 game Pyrotech on them.
I used a batch of new 5.25" unmarked disks I found in a closet; I don't remember where I got them from.
I did have some problems as it sometimes required more than one attempt to format the disks.
I tested them on a real VIC with a Commodore 1541C drive an none of them would read or format, whereas all my old, time tested disks were perfectly readable.
So it occurred to me that the batch of new disks I'd found in the closet may be high density. This would explain the issue, right? Maybe the OC-118 is slightly more "fit" and can mostly manage, but the 1541C cannot.
I've read that most DD disks have an hub ring; these disks don't have one.
Apart from data corruption, do I risk damaging the drive by using high density floppies?
Looks like I will have to dump all my old floppies on the PC and then reuse them, since I don't think double density floppies are readily available these days.
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ral-clan
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Re: High density

Post by ral-clan »

New old stock DD disks are still available. You can get them here:
http://www.floppydisk.com/

Also, you're right. HD disks are not supposed to work properly in DD drives. This is due to there being a different magnetic particle coating on the surface of the disks that takes a different magnetic coercivity (the resistance of a magnetic material to changes in magnetization). Like the difference between Type I Ferrous Oxide and Type II Cromium dioxide cassette tapes.

Your DD drive head doesn't put out the right magnetic "strength" to properly write to these disks. Sometimes it might work, and sometimes it will fail. Sometimes it will seem to work for a while but the disks will fail in time.

At least this is the theory. Some people have reported luck. On my Amiga with it's DD 3.5" drive I would use HD PC disks and they seemed to work fine for a long time.

I don't think you can harm your drive, though, by using HD disks.
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Re: High density

Post by eslapion »

LoadError wrote:I did have some problems as it sometimes required more than one attempt to format the disks.
Trying to format them on a 1541, 1541c or 1571 can destroy the read/write head of the drive.
Be normal.
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Re: High density

Post by LoadError »

Oh no!!!
I may have already, then :oops:
Before I realized I was using the wrong media, I formatted more than a dozen HDs... :oops:
Then today I found some old DDs and wanted to transfer them to D64 files in order to reuse them.
I successfully copied a few with CBM Transfer, then I started having errors on a disk.
I tried again with the disks I'd already successfully copied, and found out I couldn't read those anymore either.
I tried to open the drive to have a quick peek, hoping to clean the head, but I found out that to access it it's not enough to just unscrew the lid like with the 1541 (the Oceanic has a bottom lid).
In the end I used the OPEN15,8,15:PRINT,#15"I:":CLOSE15 command to "reset" the head and it worked for a while, then the errors came back again.
The last time I resorted to blow some compressed air in the disk opening, and this also worked.
I let it rest for a few hours, now it seems to be able to read all the disks again (bar those that caused the errors, which I ditched). I also formatted one of them and wrote stuff to it: the first time I couldn't write past a certain block; so I formatted it again and this time I was able to fill the disk.
I am hoping that the problem here is just that these old disks have soiled the head, or I wouldn't explain the compressed air workaround. Anyway these errors only started after I started using the old DDs in place of the new HDs.
But can you elaborate on how HD media can destroy a 1541 head? I need to know... :oops:
EDIT: I've just ended a burst session of reading - writing - loading (in VICE) these DD disks, no errors. It even managed to download an endless "Raid Over Moscow" disk. Hoping for the best...
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Re: High density

Post by Kakemoms »

eslapion wrote:
LoadError wrote:I did have some problems as it sometimes required more than one attempt to format the disks.
Trying to format them on a 1541, 1541c or 1571 can destroy the read/write head of the drive.
Really? Can you elaborate or give a link to that information? Using a writehead with a different magnetic layer shouldn't do much, but I recon the read process can build up a transient field in it.. Which should disappear over time?
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Re: High density

Post by Mike »

Other than a DD drive cannot reliably write on HD disks due to the reasons already laid out in the thread, I'd be very surprised to see a permanent damage done to DD drive (heads) from HD disks.

What I've seen in those times though - and this strictly refers to 3 1/2" DD drives and HD disks: I had some HD disks, which were "down-formatted" to DD capacity, and subsequently were supposed to be used (for read access only!) in a DD drive. Turned out, the higher magnetisation of the HD disks led to higher read currents, and this overloaded the read amplifier in the DD drive, resulting in lots of read errors. Yet those HD disks worked fine again in HD drives afterwards, likewise the DD drives continued service with DD disks.

That being said, when you're unlucky, the magnetic layer of an old disk just comes off (tell-tale sign: white stripes on the disk when viewed in translucent lighting), putting lots of dirt on the head, and subsequently ruining all other disks inserted in panic for tests, when the user didn't clean the drive head inbetween ...

See also:

DD vs. HD 5.25" Disks for a 1541

The mystery of HD floppies resolved?
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Re: High density

Post by LoadError »

Is there anything that was not discussed before on these boards? :lol:
I am relieved... and the drive is still working OK today. Thanks
The only drawback is I have broken the seals. I have voided the 1989 warranty :lol:
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Re: High density

Post by eslapion »

Kakemoms wrote:
eslapion wrote:Trying to format them on a 1541, 1541c or 1571 can destroy the read/write head of the drive.
Really? Can you elaborate or give a link to that information? Using a writehead with a different magnetic layer shouldn't do much, but I recon the read process can build up a transient field in it.. Which should disappear over time?
and
Mike wrote:Other than a DD drive cannot reliably write on HD disks due to the reasons already laid out in the thread, I'd be very surprised to see a permanent damage done to DD drive (heads) from HD disks.
AFAIK...
The R/W head of a disk drive is a magnetic coil just like any inductor with a reactive impedance and this limits the amount of current which can flow through the coil assuming the AC current is signaled at a consistent frequency.

This reactive impedance (aka reactance) is dependent on the materials comprising the inductor and in the case of the R/W head of a disk drive, the floppy disk magnetizable material is part of these materials. Using a HD floppy in a DD drive has the effect of considerably reducing the reactive impedance and increasing the current flowing through the R/W head when writing data to the disk.

AFAIK, the destruction of the R/W head can occur when, in a panic, someone tries multiple times to format an HD disk.

From Wikipedia:
Reactance is measured in ohms but referred to as impedance rather than resistance; energy is stored in the magnetic field as current rises and discharged as current falls. Inductive reactance is proportional to frequency. At low frequency the reactance falls; at DC, the inductor behaves as a short-circuit. As frequency increases the reactance increases and at a sufficiently high frequency the reactance approaches that of an open circuit.
Be normal.
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Re: High density

Post by LoadError »

Do you actually mean the head itself can be damaged? Or the amplifier circuit mentioned by Mike?
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Re: High density

Post by eslapion »

LoadError wrote:Do you actually mean the head itself can be damaged? Or the amplifier circuit mentioned by Mike?
The amplifier is used on reading but I suppose both could be affected by a reduced reactance.
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Re: High density

Post by LoadError »

I'm no expert but it sounds like something that might happen in the long run and/or under extreme circumstances.
Anyway, it looks like the OC-118 is one hell of a disk drive. Other than being back to normal with just a blow of compressed air from the outside, it was able to format, read and write to HD media whereas my 1541C refused to even think about it. :D
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Re: High density

Post by LoadError »

Breaking news: at my office I've found two packs of 10 5.25" disks labeled "Magnum MD1D - Hub Ring - single side - double density - soft sectoring".
Still SEALED in their plastic bag and jewel case!
I wonder if I should use them or sell them :D
Bonus: look what lies next to them (not for sale) 8)
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Re: High density

Post by ral-clan »

I know someone who actually got a whole load of DD disks at his work, when they recently emptied a storage closet and ended up throwing out many old corporate copies of WordPerfect and Lotus 123 for MS-DOS from the 1980s. Each software package contained about 4 disks, and other than being used once to install the application to a hard drive, the disks were put back in the box and never ever used since.

There was no visible indication on the disk that these were DD capacity, but they were formatted to 360K capacity (which was identified with a DIR command).
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Re: High density

Post by siccoyote »

I had a similar problem, I am sure in the past I had LOADS of Sd/dd floppies in the house, but maybe 10-15 years ago got rid of them as they were in my eyes obsolete. Now I want to use my floppy drive and the only disks I could find were a box of HD floppies which my 1541 did not like at all.

I am sure I still have some around somewhere, but my collection is such a mess I will have to spend much time hunting for them, or I could buy some new ones, but shocked at some of the prices for them online.


I was quite pleased though that after 10-15 years of sitting on a shelf and being shifted between boxes, my 1541 still loaded Stunt Car Racer and Return of the Jedi on the c64 with no problems.
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Re: High density

Post by Kakemoms »

eslapion wrote:AFAIK...
The R/W head of a disk drive is a magnetic coil just like any inductor with a reactive impedance and this limits the amount of current which can flow through the coil assuming the AC current is signaled at a consistent frequency.

This reactive impedance (aka reactance) is dependent on the materials comprising the inductor and in the case of the R/W head of a disk drive, the floppy disk magnetizable material is part of these materials. Using a HD floppy in a DD drive has the effect of considerably reducing the reactive impedance and increasing the current flowing through the R/W head when writing data to the disk.

AFAIK, the destruction of the R/W head can occur when, in a panic, someone tries multiple times to format an HD disk.
Interesting. Its possible that high currents can drive some components to destruction, but probably only if it also generates higher voltage. It would be an interesting experiment to see how large these (current and voltage) gets for each case (DD vs HD).
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