dencorso, on 25 September 2011 - 01:53 AM, said:
the coercivity and the strenght of the magnetic field used need not necessarily to be matched. On the contrary, using HD media to record low density formats works OK, although it's an overkill. Media with higher coercivity will hold weaker magnetizations just as well as it does higher magnetizations, but the other way round is not true. So trying to format DD media to 1440 kiB results in bad clusters galore appearing fast, in a matter of a few days at most, in the very rare cases they don't appear right away, during the format operation. But formatting HD media to 720 kiB is just as safe as formatting DD media
Over the years, the company I work for has supplied numerous pieces of software for our customers, which at one time, was distributed on floppy media. So we have (had) experience in copying many thousands of diskettes, sourced from a variety of vendors. Because it could be read by both types of drive, our practice was to standardize on the 720K format, even after 1440K drives became the norm. However, as 720K media became less common, we started to use 1440K media, unaware this would be a problem. So we learnt "the hard way" that this isn't reliable. Depending on the particular drive, and especially the make of diskette, we had the situation where HD diskettes would even fail the verification stage immediately
after being copied (in 720K format). We might have assumed that this was a quality problem with the diskettes, except that these were actually from a very reputable manufacturer. So I raised this matter with the manufacturer, which is how I learnt about this coercivity issue. And just to confirm what manufacturer had said, we retested the "bad" diskettes in 1440K format, and they worked perfectly.
jaclaz, on 25 September 2011 - 03:12 AM, said:
I will repeat myself:
jaclaz, on 23 September 2011 - 08:38 AM, said:
There is no actual difference in the internals of a floppy disk (at least between the 720 and the 1440) and I know for sure that for at least a short period around 1994/1995 ONLY 1440 floppies were produced and they were "packed" into either a "single hole" plastic case (720 Kb) or in a "two hole" one (1440 Kb).
I have physically seen myself a line of production for floppies that worked as above stated.
I don't think that the manager of the factory rearranged the facility expecially the day I visited it in order to hide some manufacture secret.
So, to be more exact, I have reasons (direct experience) to affirm that at least one factory in the world in a period approximately between 1994 and 1995 used the SAME magnetic media on both the 720 and the 1440 diskettes.
Apart from the above, that may have been a black swan
of some kind
, and due to the fact that the period in which I have visited the factory was towards the end of the actual common use of the 720 floppies, and thus some "shortcuts" may have been used by the manufacturer, please read this:
As you can see, the results in real life are controversial, and we have both a statement like:
What about storing DD data on a HD disk? The grains are small
enough for the data, in fact smaller than they need to be. However, DD
recording strength is twice HD recording strength. Recording DD data on a
HD disk will force the data into the grains, like using a pencil with too
much pressure. It will be difficult for the recording head to erase old
data to write new data over it. The data on the disk will deteriorate
every time something is written to it.
And one like:
I've gotten plenty of conversion work where the 3.5" floppies were a mixture of HD and 2D media written in 2D drives ("720K" drives are blind to the media sense hole in a 3.5" jacket). Usually, they're just fine, with the error rate approximately the same, whether or not 2D or HD media was used.
My personal experience is actually similar with the last quoted statement but I guess that there is also a factor connected to the actual hardware (floppy disk drive maker/model).
Well, back in the day when we had both DD and HD diskettes from the same manufacturer, we could distinctly see a difference in the coating of the disks. So your manufacturer either didn't care (or was careless), or else they developed a compromise formulation that was somewhere between DD and HD and used this for both.
Did you ever stop to think, why did the manufacturers introduce that extra hole in the shell to distinguish DD from HD? Do you think it's because they could charge a higher price for HD? No, it's because of similar issues encountered, and lessons learnt, from the 5.25" era.
I can agree with your last sentence. So what's your definition of "reliable"?
This post has been edited by jds: 25 September 2011 - 09:15 AM