[Coco] Dead (??) 5 1/4" drives

[Gene Heskett]

On Wednesday 08 March 2017 11:41:05 Bill Gunshannon wrote:

> ________________________________________
> From: Coco [coco-bounces at maltedmedia.com] on behalf of Mathieu
> Bouchard [matju at artengine.ca] Sent: Wednesday, March 8, 2017 8:44 AM
> To: Barry Nelson
> Cc: coco at maltedmedia.com
> Subject: Re: [Coco] Dead (??) 5 1/4" drives
>
> Le 2017-03-06 à 23:50:00, Barry Nelson a écrit :
> >> I have 2,  5-1/4 drives, of which one can go. ( keeping at least
> >> one for myself). I do think they are both DS 80 track drive's, and
> >> they where given to me from e working setup. If you are interested
> >> in one let me know.
> >> I think that $20 + Shipping would be a reasonable price.
> >
> > DS 80 track? That would make those 720k drives.
>
> Nope, because 3.5" DS 80-track includes three different densities :
> 720k, 1440k, 2880k. They are distinguished by number of sectors : 9,
> 18, 36 (with PC formatting @ 512-byte/sector).
>
>  
> ______________________________________________________________________
>
>
>
> As long as we are talking floppies and formats, I have a question
> before I actually try anything.
>
> The WD1773 is capable of higher densities than 128 and 256 byte
> sectors. Is ther any harware reason why the COCO can't make use of
> them?  Is it too slow?  If so, what about in Turbo Mode?
>
> I am still trying to fiond a way to use generic USB Stick floppy
> emulators and right now the problem seems to be that they are all 512
> byte sectors and can not (easily) be coaxed into anything smaller.
>
> Is the density actually set in the driver or DOS code or is it somehow
> hardwired?
>
>
> bill

With the superdriver, it is not hard wired. A switch bit in the 
descriptor tells rbsuper to either read the sector's 512 bytes and hand 
os9 the first 256, wasting half the storage capacity, or if the bit is 
set, it will give os9 either half on the sector after dividing the 
address by 2 by a right shift, saving the shifted out bit so if its 
clear you get the first half of the sector, and if its set, the last 
half of the same sector.  Works perfectly, I've used it since forever it 
seems.
Cheers, Gene Heskett
-- 
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