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Old 20 September 2009, 22:18   #21
Graham Humphrey
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Originally Posted by prowler View Post
A further problem is that some users - Boo Boo, for example - have no difficulty at all in using HD disks in DD drives!
Me too. I've got some HD disks that are years old but still work perfectly in my A1200. Just to muddy the waters still further.
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Old 21 September 2009, 16:17   #22
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Disk related, but still off-topic:

When are people going to realize that DD disks are 1 megabyte, and HD disks are 2 megabytes As far as I know the Amiga disk drive controller can actually use a DD completely

Thank you for baring with me. It's just that I see incorrect disk sizes 'all over' the net.
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Old 21 September 2009, 16:24   #23
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When are people going to realize that DD disks are 1 megabyte, and HD disks are 2 megabytes As far as I know the Amiga disk drive controller can actually use a DD completely
Don't bother us .......... only joking .
You're right, ok, but... 1MB (DD) and 2MB (HD) are the unformatted capacities of the medias.
Oookey, if U want to be picky then let's be picky
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Old 21 September 2009, 17:46   #24
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Quote:
Originally Posted by Thorham View Post
Disk related, but still off-topic:

When are people going to realize that DD disks are 1 megabyte, and HD disks are 2 megabytes As far as I know the Amiga disk drive controller can actually use a DD completely

Thank you for baring with me. It's just that I see incorrect disk sizes 'all over' the net.
incorrect disk size ? If an ADF is bigger than 901120, it's an extended ADF,
meaning the software holds a copy protection.
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Old 21 September 2009, 17:49   #25
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Not necessarily as thomas said here : http://eab.abime.net/showthread.php?p=595147#post595147
I love to learn new facts about the Miggy
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Old 21 September 2009, 17:57   #26
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How do you know the quality is higher? I bet all your DD disks are 15 years older than your HD disks Even if they're not, I'd need some kind of proof of manufacturing process quality

Anyway, can we file this as (final?) evidence to all the jerks who claim using HD disks for DD Amigas is fine please.

I have no problem with HD disks, writing them either in the amiga or cyclone, you just have to cover the tab. ?


Quick edit: Maybe its because all the drives i use are PC drives modded for amiga use rather than a "Official" Amiga drive... who knows ?

Last edited by kipper2k; 21 September 2009 at 18:05.
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Old 21 September 2009, 17:58   #27
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HD disk on amiga are unreliable. Got many of them not working anymore after a few times.
Use DD with DD drives.
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Old 21 September 2009, 18:50   #28
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Hmmm, interesting! This could be the right reason!
It makes sense.



No, I don't think you're right... An unformatted disk has no "predefined" bits. It's only a layer of magnetic surface.
It's not like a CD-R, which has a physical spiral on which the burner will lay down the bits (the "0" and "1" sequence) with a certain frequency (/distance between bits).
A DD head (or HD head in DD mode) which will write on a HD disk will not have to switch bit states twice as fast! It will format the disk with a same structure (and bit density) as it would when writing to a DD disk.
Furthermore, there will be no "bits inbetween". The surface is *all* written/formatted, all (DD) bits are written. Simply, the denser surface is not used at its best.

It's similar to when you format a 5,25 floppy with a 40-tracks drive or an 80-tracks drive. In both cases the whole surface is formatted. There'are no unformatted tracks inbetween.
What is different is the "radial width" of the tracks: tracks written by a 40-tracks drive are bigger (circa twice) than those written by an 80-tracks drive.
Yes, confusingly enough, there's arguments in both directions. Do you have a HD drive maybe? See below.

I think HD disks spin at the same speed with a doubled data bitrate to the head (but ofc the material itself must also be able to switch magnetic state faster.)

The below are thoughts separate from the currents- and other electrical differences between the drives.

Now, during the longer time that a DD drive magnetizes a "slow" material, you get a "wide" stretch of material that is magnetized pos/neg. Both a DD and HD disk can read it reliably, but if the HD drive expects HD data, each bit will be doubled. Now, that was kind of a lie. This is MFM. Which means it reacts to time between CHANGES only. So a HD drive will simply get half the bits it expects, but the same data. If the software recognizes it, it will say "DD OK" and all is fine.

However, a DD drive should have trouble reading DD data written on a HD drive on a HD disk, for reasons Thomas kinda hinted at. Data will be written and verified fine, but the quicker periods of magnetization will not be as the DD drive expects them. If there is any gap at all, a sequence of 1_0_1_0_1_1_0_1 could become "1r0r1r0r1r1r0r1r", where "r" is "magnetic state undefined/unchanged". The DD drive that tries to read a "1_" (long 1-bit) could get "1r" or "r0" due to losing its "bitsync" from the random interference.

A HD drive writing a DD image on a DD disk, on the other hand, will probably fail to verify right away in the HD drive. Depends on the current (strength of magnetic field) the drive delivers, and if the DD disks have the more easily magnetizable material. I.e.: Non-cheap (full HD+DD support) drives made for PC (or same specs) and new DD disks made for PC "1.44mb" drives should produce usable DD disks (but no other drive-disk combination). That is, writing ye olde DD disks from 1989 in any HD drive will likely fail due to the material.

The last case is a DD drive writing a DD disk with either material (new for PC-driver or old), which should be fine and dandy - even though new ones could possibly have a material "adapted towards HD", due to the manufacturers not wanting to have two manufacturing processes but use the same material for both. If so, then it's more easily affected outside the drive.

I've written so much I'm confusing myself, hehe... the case talked about here (if you verify if you have a HD or DD drive), writing DD on HD-disks in a DD drive, should work fine, really.

Except (by empirical evidence) it's hit-and-miss. All I can think of is that it's the material varying from disk brand to disk brand. Which means you should buy/use DD disks to avoid wasting time

Last edited by Photon; 21 September 2009 at 18:58.
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Old 21 September 2009, 20:15   #29
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Not necessarily as thomas said here : http://eab.abime.net/showthread.php?p=595147#post595147
I love to learn new facts about the Miggy
I'm not certain of those 'facts'.

I removed the 'last two tracks' from that ADF image and wrote the resulting 901,120 bytes image back to disk. The disk thus produced was not only bootable, but was also visible in Workbench and diskcopied OK.

That image is still in the Zone.
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Old 21 September 2009, 20:31   #30
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Even if this disk only has garbage on track 81 and 82, this proves that they can be written back : http://eab.abime.net/showthread.php?p=595264#post595264. Just wanted to point out that not every >880k floppy is protected or 'extended'.
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Old 21 September 2009, 20:36   #31
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Even if this disk only has garbage on track 81 and 82, this proves that they can be written back.
The Amiga is not alone in allowing data to be written to tracks 81 and 82. The PC also allows a number of extended formats which use these tracks on both DD and HD disks. The limiting factor in these circumstances is the floppy drive itself.
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Old 21 September 2009, 21:11   #32
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You're right, ok, but... 1MB (DD) and 2MB (HD) are the unformatted capacities of the medias.
What I mean is that on a DD disk you can store one megabyte of data. Formatting only writes a filesystem structure to the disk, and that is data as well. A standard AmigaDos formatted DD disk still doesn't amount to a megabyte of data when you include the file structure, and there is actually a filesystem available for AOS which allows you to format a DD disk as one megabyte, although the filesystem structure will use up some of the space

I think Amiga User International used to use that filesystem for some of their cover disks.
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Old 21 September 2009, 21:40   #33
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What I mean is that on a DD disk you can store one megabyte of data. Formatting only writes a filesystem structure to the disk, and that is data as well. A standard AmigaDos formatted DD disk still doesn't amount to a megabyte of data when you include the file structure, and there is actually a filesystem available for AOS which allows you to format a DD disk as one megabyte, although the filesystem structure will use up some of the space

I think Amiga User International used to use that filesystem for some of their cover disks.
I perfectly understood what you mean .
I didn't disagree with you and I'm sure: 1MB (DD) and 2MB (HD) are the unformatted/max capacities of the medias. You can also read it on some floppy packages: "1MB unformatted" etc.
As you wrote: "DD disks are 1 megabyte, and HD disks are 2 megabytes".

http://en.wikipedia.org/wiki/Floppy_disk

"Floppy disk drive and floppy media manufacturers specify an unformatted capacity, which is, for example, 2.0 MB for a standard 3½-inch HD floppy. It is implied that this data capacity should not be exceeded since exceeding such limitations will most likely degrade the design margins of the floppy system and could result in performance problems such as inability to interchange or even loss of data."

"User available data capacity is a function of the particular disk format used which in turn is determined by the FDD controller manufacturer and the settings applied to its controller. The differences between formats can result in user data capacities ranging from approximately 1300 KB up to 1760 KB (1.80 MB) on a "standard" 3½-inch High Density floppy (and even up to near 2 MB with utilities like 2MGUI). The highest capacity techniques require much tighter matching of drive head geometry between drives; this is not always possible and cannot be relied upon."

Last edited by Supamax; 21 September 2009 at 21:49.
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Old 23 September 2009, 00:11   #34
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Well I've just found a box of new unused 2HD floppies in a draw, I'm going to have a bit more of a play with these new disks given all the posts above lead me to the conclusion that if I write the ADF with my left leg raised to a height of 30cm and facing west then it might just work.
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Old 23 September 2009, 03:44   #35
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given all the posts above lead me to the conclusion that if I write the ADF with my left leg raised to a height of 30cm and facing west then it might just work.
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