Re: Disk II Half - Quarter Tracks

[Tristan Mumford <xtristan.xmumford@xgmail.xcom>]

Michael J. Mahon wrote:

> Tristan Mumford wrote:
>> Michael J. Mahon wrote:
>> 
>> 
>>>RedskullDC wrote:
>> 
>> -snip-
>> 
>>>>I did once experiment with the track widths to see what could be
>>>>achieved.
>>>>
>>>>Using a stock standard Disk][, writing on every half track proved to be
>>>>unreliable.
>> 
>> -snip-
>> 
>>>>The DOS3.3 track stepping routines would need to be modified to support
>>>>3/4 track spacing, but it would be possible to easily gain an extra 50%
>>>>storage capacity
>>>>on a disk][ this way.
>>>
>>>Actually, just 33% more data--and likely *much* less reliability.
>>>
>>>
>>>>Differing results may be obtained using different disk][ drives, as I
>>>>have no idea of
>>>>the manufacturing tolerances of the read/write head widths.
>>>
>>>Right.
>> 
>> 
>> Agreed. There _is_ another option that has crept into my deepest, darkest
>> thoughts though.
>> Using a different type of drive. Looking at the disk ][ etc. signals it
>> doesn't seem completely out of the realm of possibility to connect a PC
>> drive to a disk ][ style controller. For instance, every stepper I have
>> seen on a PC drive has the 4 phases(?) exposed without dismantling, at
>> least much anyway.
>> Blah blah... proprietary drive that nothing else could read ... blah.
>> Anyway my point is that utilising something designed for higher density
>> would allow it. The main question would be head voltage. Higher densities
>> usually use lower voltages.
> 
> But the head is controlled by in-drive electronics, so that shouldn't be
> a problem for the controller.  And virtually *all* floppy drives predate
> 3.3v logic.

I haven't seen a 3.3v one yet. Although notebook ones may be.
I was referring to what is applied to the read/write head. It is my probably
flawed understanding from what I have read that the higher densities use a
lower voltage. This is to stop track crosstalk etc for higher ones, and to
accommodate the lower density disks which may not read correctly at the
lower voltage (probably something to do with narrower magnetisation too).

> 
> The bigger problem is the bit rate.  The Disk ][ controller is designed
> around a 250kHz bit rate, and higher density drive all used much higher
> bit rates.
> 
> More tracks would still improve capacity, but you'd be stuck with low
> bit rates.  Of course, since we're talking custom modifications here, it
> might be possible to lower the rotational rate along with the bit rate
> to get more bits per track...

Precisely. I was reading in some unknown place a while back about this sort
of thing. I see no reason why one can't replace the crystal to achieve
the 'correct' rotational rate for the drive. I just wish I remembered where
I was reading this.

Do the older mac drives change the rotational rate or the sampling/writing
rate for the different tracks? Not considering them. Just curious.

Or I guess another solution is to take the head from a higher density drive.

...or SCSI, or CF, or USB*

*There are a few people working on different projects to achieve this.
Myself included. The difference is my test rig runs via RS232. Future
versions will be not unlike the others once the double sided blank pcb
arrives.
I guess not everyone has an extra SSC in their apple anyway. Besides, I
wouldn't have a clue how to make a ProDOS driver work in RAM for use via
another driver. Shame.
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