[Coco] Re: POKEd floppy access

Arthur Flexser flexser at fiu.edu
Wed Apr 26 15:29:17 EDT 2006

You're thinking of cassette, where tapes written at double speed can only
(without special techniques) be read at that speed.  Disk I/O works fine
if you save at high speed and read at low speed, if the ROM has been patched for
longer delays.


On Wed, 26 Apr 2006 farna at att.net wrote:

> IIRC ADOS would "fix" the double speed drive access "problem". I ALSO seem
> to recall that if you write a disk at double speed, you can read it ONLY AT
> DOUBLE SPEED. Try slowing the CoCo back to normal speed and reading a disk
> you wrote at double. I bet it won't! The only problem is you have to
> remember to speed up to read those disks.
> When I wrote a genealogy program for the CoCo 3 (needed the wide display
> screen) it was pretty fast because I used every trick I could find --
> including double speed. But for disk I/O there was a line to slow it back
> down before and a line to speed back up after. The disks may have been fine
> at double speed, but would have been unreadable if someone wanted to use the
> data in another program unless they knew to speed the computer up. I
> definitely wanted the disks to be as reliable as possible for data storage
> though, especially since the records were prewritten to the disk, not formed
> as they were created. That's another trick that made the program pretty fast
> for a data base -- it just filled in blanks that were already there (a
> "create data format" program formatted the data disk). The drawback to this
> method was if a sector went bad i corrupted the disk up to the bad sector.
> Anything written beyond would be lost. People were encouraged to make
> regular backups.
> -- Frank Swygert Publisher, "American Independent Magazine" (AIM) For all
> AMC enthusiasts http://farna.home.att.net/AIM.html (free download
> available!)
>  -------------- Original message ----------------------
> > Date: Tue, 25 Apr 2006 19:30:26 -0400
> > From: Diego Barizo <diegoba at adinet.com.uy>
> > Subject: Re: [Coco] POKEd floppy access
> > 
> > Just regular "RS-DOS".
> > Could be that changing the step rate of the drives has any effect in 
> > this area?
> > 
> > Diego
> > 
> > 
> > Robert Gault wrote:
> > 
> > > Just depends on the values in certain timing loops in DOS. Some third 
> > > party DOS were written to handle disk I/O at 2MHz. What DOS are you 
> > > running?
> > >
> >
> -- 
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