Re: Disk II Half - Quarter Tracks

["Alex Freed" <alexf@mirrow.com>]

"Tristan Mumford" <xtristan.xmumford@xgmail.xcom> wrote in message 
news:45cd15b6$0$83726$c30e37c6@lon-reader.news.telstra.net...
>>
>> 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 don't think that's an issue at all. Consider the standard PC/AT type 1.2 
MB
5.25" drive. It can handle "high density" 80 track 1.4 MB disks or "double 
density"
40 track 360K disks. Or anything else as long as it is MFM encoding.

It doesn't have to slow down - just data density is lower.
So the ABILITY to record high density data doesn't mean it can't handle 
slower data.

So this is a simple hardware mod. Maybe no extra hardware at all. Instead a 
software
patch to use 2 "motor phase" lines to control DIRECTION and STEP.

That should get 80 tracks of standard DOS 3.3 16 sectors.

-Alex.