[Coco] 3.5" Drive Variable in the NitrOS-9 Module Header

[Gene Heskett]

On Sunday 27 January 2013 14:37:04 Wayne Campbell did opine:
Message additions Copyright Sunday 27 January 2013 by Gene Heskett

> I recall that, although I never saw one, 720K floppies did exist, both
> in 5.25 and 3.5 varieties. I'm not sure it will be worth it for those,
> except for completeness as they were rare back then (89-94). I think
> the greatest issue will be the high-density drives. The 5.25 variety is
> 1.2 meg instead of 1.44 meg. Will that make a difference to the driver?
> 
> When I had my Coco3 I had 3 80-track floppies, 2 5.25 and 1 3.5. I found
> a 1.44 meg 3.5, but it was only usable as a 80-track 360K because the
> descriptors and driver wouldn't work with anything larger under OS-9
> Level 2.
> 
It bears repeating here that this is not an os9/nitros9 problem, its 
hardware related.

It is the FDC chip, the x773's used in the controllers cannot be switched 
to a 500 kilobaud data rate, only 250 kilobaud.  There are instructions 
floating about on the web on how to make the original 40 pin '93 controller 
into one that can do 500 kilobaud, and I have one with a Fujitsu MB8877A in 
it that might be worth trying to patch, but really, with drivewire, its far 
more of a 'can I do it' project than of any real use.

FWIW, that 1.2 meg format was reduced from 1.44 megs by switching the 
platter speed from 300 rpm up to 360 rpm, I assume in an effort to get 
adequate playback levels out of the then primitive heads, by both 
lengthening the magnetic wavelength on the disk, and the boost from the 
increased disk velocity.  Most, tied to a decent disk controller could 
probably be used at 1.44 megs with the disks available near the end of the 
floppies reign as a storage medium.  Don't forget too, that at the end of 
the floppies run, we had 2.88 meg floppies, where the FDC ran at 1 megabaud 
data rates.  But the hard drive grew up and kicked the floppy to the curb 
about then.


> Kip Koon <computerdoc at sc.rr.com> wrote:
> >NitrOS-9 Developers,
> >
> >I have been giving some serious thought to the recent discussions about
> >when to use a track density of 48 tpi or 96 tpi.  Here's my thoughts
> >on the matter.  Create a new bit in the Drive Descriptor which is
> >called '3.5" Drive Track Density' and this is how it would work.  When
> >this bit is set to 0 (zero) the other track density bit would be
> >active.  When set to 1 (one), the other track density bit's effects
> >are deactivated and the new track density becomes 135 tpi.  We could
> >also implement a bit called "Quad Data Density"  to take advantage of
> >the 3.5" drive's highest data density capability and finally reach the
> >full capacity of a 1.44 floppy disk drive and it could work in a
> >similar fashion.  When the bit for Quad Data Density is 0 (zero), the
> >other data density bit is active, and when the Quad Data Density bit
> >is 1 (one) the other data density bit is deactivated and the data is
> >encoded onto the floppy disk's surface using the 3.5" drive's Quad
> >Data Density capabilities.  Of course all disk drive drivers would
> >have to be updated to implement the change in the Drive descriptor
> >giving the correct commands to the 3.5" drive when appropriate.  If
> >there is space for these two new bits in the current Drive Descriptor
> >Definition, there may be the possibility that only floppy drive
> >drivers would need to be updated due to the definition that if both
> >new bits were 0 (zero) their older counterpart bits would remain
> >active and all should be well.  So guys, what do you think of my brain
> >storming session?  Do you all think that this may be possible?  So far
> >in my thoughts, it sounds very doable.  Thanks for considering my
> >suggestion.
> >
> >Kip
> >
> >
> >
> >
> >--
> >Coco mailing list
> >Coco at maltedmedia.com
> >http://five.pairlist.net/mailman/listinfo/coco
> 
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco


Cheers, Gene
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene> is up!
My views 
<http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml>
When the only tool you have is a hammer, every problem starts to look
like a nail.
I was taught to respect my elders, but its getting 
harder and harder to find any...