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Re: Best way to backup Amiga floppies

Posted: Wed Sep 30, 2015 4:12 pm
by sky76
Can 3,5" DD drives also write back KF stream tracks onto DD disks no matter whether they've been imaged with an HD or DD drive?

Re: Best way to backup Amiga floppies

Posted: Wed Sep 30, 2015 5:02 pm
by Sirswift89
So can I write Amiga disks using HD media or should I use DSDD disks on the 1.44 drive?

Re: Best way to backup Amiga floppies

Posted: Wed Sep 30, 2015 10:12 pm
by BarryB
The manual states:

"Use genuine DD disks if you are writing DD data. Do not use HD media with the detection
hole covered unless you know what you are doing."

So NO, do not use HD Disks for DD data!

Re: Best way to backup Amiga floppies

Posted: Thu Oct 01, 2015 6:30 am
by sky76
Even back in the old days I had the feeling that HD disks are more likely to generate errors when written & read with DD floppy drives (on real Amigas) than DD disks (unless you had an A4000 with HD floppy drive).

People are still selling(!) DD disks all over the place, but I'd better not buy nor use one of these disks because you never know how they've been stored. I have 1500 DD disks stored at room temperature in cupboards for the last 20 years and they are of much better condition than most of these rotten DD disks you'll get when you buy vintage hardware on the net.

Still, real floppies are probably dying out soon and may only be used if really needed. For long term storage I'd never recommend them, but they may be good enough for playing with the "real retro feeling" whatever this means to each of us individually. I still love the sound of an A500 floppy drive - as long as it's a fast loading 1- or 2-disk game. ;)

Re: Best way to backup Amiga floppies

Posted: Fri Oct 02, 2015 12:40 pm
by IFW
sky76 wrote:Can 3,5" DD drives also write back KF stream tracks onto DD disks no matter whether they've been imaged with an HD or DD drive?
Yes; when you read a disk the DD/HD mode changes the gain/filtering applied to the analog data - if it does anything at all. Sadly many drives don't implement proper DD filtering during reading, as most of the time you can get away with HD only; you only get problems with longer than usual flux reversals, ie custom formats used by commercial games or some 8 bit computer systems :roll:
So most of the time the data you read with a DD or HD filtering is identical.
Where you can get differences is if very long flux reversals used by design (typically C64 and Apple disks) or unformatted areas. HD filtering would trigger lots of false flux reversals detected for unformatted tracks and areas (due to gain/sensitivity/threshold differences), whilst DD would not.

Due to this you may be able to read out DD data correctly in HD mode that is unreadable in DD mode, however, you may have trouble reading out perfectly good data as well, as glitches (filtered in DD) can easily become flux reversals in HD.

Essentially, you should sample DD disks in DD mode (if the drive has a genuine DD hw read mode at all...) and use HD mode specifically on tracks where the data is unreadable otherwise.
This way you can:
- keep the falsely detected flux reversals to minimum
- make your stream file archives much smaller (unformatted tracks will compress very well if sampled as DD, due to less random noise generated)

This advice is mostly useful for 5.25 disks, since the drives have no media type sensors.

On the other hand, that 3.5 drives auto-detect the density of the disk using the media hole.
You should never alter the real type of the disk by changing the media type - unless the disk was originally written that way :lol:
e.g. one of my very old Amiga backup disks was written on a HD disk and of course unreadable in a real HD capable PC drive, since the disk was detected (properly) as HD. Putting a sticker over the media hole "made it" DD, and now it became fully readable by the drive as the media type became correct for the filtering.

Re: Best way to backup Amiga floppies

Posted: Sat Oct 03, 2015 4:42 pm
by sky76
Thank you for this good explanation!

So this is THE way to go: Use a DD drive for reading 3,5" DD disks and also for writing them back to 3,5" DD disks.

Reading 3,5" DD disks with an HD drive could cause glitches to be detected as flux reversals. Writing back to 3,5" DD disks with an HD drive could be ok.

Re: Best way to backup Amiga floppies

Posted: Sat Oct 03, 2015 6:36 pm
by IFW
My explanation was mostly for 5.25 drives, due to their lack of media type detection.
3.5 HD is fine for everything as long as DD is actually supported.

Re: Best way to backup Amiga floppies

Posted: Wed Apr 10, 2019 3:47 pm
by Vipersan
Hi ..
I'm in exactly the situation being discussed here.
I have original Amiga games which I fear may be coming to end of life re the floppies ..and would like to get them cloned/preserved by dumping them(copy protected) as raw images ..and written back to new old stock floppy disks ..
I have tried doing this with my KFB already but had no success (using the GUI) ..
I'm guessing I have to go to command line to achieve this ..but sadly am clueless in this regard.
Could someone kindly instruct me or better still provide me with the correct command line syntax to achieve my goal.
kind regards
VS

The actual floppy drive I'm using is a Standard 3.5 inch internal floppy disc drive, FDD by Sony.
not sure of model number.

Re: Best way to backup Amiga floppies

Posted: Thu Apr 11, 2019 6:23 am
by sky76
Hm. What would be the difference between "writing back" an "official" IPF image versus "kryofluxed" stream files of a copy-protected Amiga 3,5" disk using DTC in the command line? Is it even possible to write an IPF back to disk using DTC?

Re: Best way to backup Amiga floppies

Posted: Thu Apr 11, 2019 8:00 am
by brightcaster
What would be the difference between "writing back" an "official" IPF image versus "kryofluxed" stream files of a copy-protected Amiga 3,5" disk using DTC in the command line?
The main difference is that ipf images can be verified after writing and they are strictly "formated" (the gap is at the position of the index for example). If you write back a stream you write one revolution from index to index no matter where the gap is.

Now keep in mind that the amiga os doesn't care about the index. The chance that the gap appears exactly at the index position is very low. Most likely, the index is in the middle of a sector. Due to mechanical tolerances, starting and stopping the writing procces in the middle of a sector will result in either an overlap or an additional gap. That makes the track unreadable...
Is it even possible to write an IPF back to disk using DTC?
You can write adf, g64, ipf and raw streams so far...

David