Re: C900 floppy format.

The Oersted value refers to the magnetization curren required. That is the
same for SD/DD/QD disks anyway.

Where it gets interesting ist the specified bits per inch.

This is actually the same for SD and DD and QD. SD & DD use a bpi of
5900bpi that translates to a 250kHz clock.


The big CBM floppies used 375kHz but were still specified for DD. I think
they cheated...


André

Am 21. Oktober 2020 11:23:16 schrieb silverdr_at_wfmh.org.pl:

>> On 2020-10-21, at 10:55, Francesco Messineo <francesco.messineo_at_gmail.com>
>> wrote:
>>
>>>> there's no "QD" magnetic media, SD/DD/QD magnetic media was always the
>>>> same (300 oersted).
>>>
>>> Right, but AFAIU that's not the point
>>>
>>>> Probably the diskettes sold as QD/96 tpi were just higher quality.
>>>
>>> Delivering higher resolution without changing the magnetisation
>>> characteristics. Similar to "Type I" in analogue audio tapes. One used the
>>> same oersteds/bias/eq for different tapes of the same "Type I" but the
>>> results could be _hugely_ different between different tapes.
>>
>> in the case of floppy disk drives, it was a better (smaller) head
>> design and a much better head positioning stepper and mechanics. The
>> design of 96tpi and 100tpi drives started by using the old available
>> magnetic media. Then after that,  floppy disk manufacturers thought
>> they would make more money if they advertised their standard media as
>> "QD" and 96tpi certified. As they already did the same then MFM and
>> double density was introduced, with always the same magnetic media
>> that was used with FM modulation (called single density).
>> I still have boxes of very old floppies sold as single density.
>> I would not compare analog cassettes to floppy disks.
>
> Why not? It's the very same idea and principle. You could have magnetic
> medium that was not able to record enough density (higher frequencies) and
> you could have another one which was. Both having the same magnetisation
> parameters. The same here - you can have a medium, which is capable of
> recording higher frequency (density) and you can have one, which is not.
> Heads and co. play an important role too, which – BTW – applies to analogue
> tapes as much as it does for disks, but the underlying principle is the
> very same in both cases.
>
> Also, I don't say that what you assert about vendors making money with
> marketing buzzwords is incorrect. It most probably is. What I object to, is
> that you _directly_ link the magnetic characteristic (300 oersted) with
> with the achievable resolution (density). This is neither true for disks
> nor for tapes. For the very same reasons in both cases - something you
> called "quality".
>
> What it should be with "QD" floppies is that they should be tested and
> certified to be capable of delivering higher resolution. That doesn't mean
> that "DD" medium is automatically not. It's just that it wasn't certified
> for that.
>
> How it was in reality - I don't know but I can imagine the vendors slapping
> the marks at will while being relatively sure that nobody will sue them if
> _some_ of those media do not perform.
>
> --
> SD!