[Coco] Read coco disks on a PC

[gene heskett]

On Thursday, March 15, 2012 10:29:04 AM John E. Malmberg did opine:

> On 3/15/2012 7:59 AM, Bill wrote:
> > Please excuse a dumb question, but what software would I need to
> > read/write Coco disks on my PC?
> 
> There are a few tools out there.  I am sure by the end of the day
> someone will give you several links.
> 
> Prior to Windows 2000/XP you could write a program on MS-DOS to override
> the BIOS settings and read/write 256 byte sector disks, so it was easy
> to write a program to read/write such disks.
> 
> With Windows XP that API has been removed.
 
And in many more 'modern' motherboards, the resident superio chipset that 
does the floppy controller duties, no longer supports ANY 256/sector 
formats.

> A CATWeasel board/adapter if you can find it and afford it, + software
> will allow reading/writing many old formats.

I haven't seen one of those for sale in yonks.
 
> I did an experiment a few years back and discovered that the COCO BASIC
> disk read/write routines could read/write sectors on MS-DOS formatted
> 512 byte double density disks.
> 
> Internally BASIC allocates 256 bytes for reading/writing to the disk and
> another 256 bytes for verification for a total of 512 bits.

Correct bits to bytes above.
 
> As long as you do not turn on verification you have 512 byte buffers.
> 
> BASIC does not keep track of how many bytes are read in, it depends on
> the controller hardware to interrupt a tight loop that is reading or
> writing bytes to the controller.  So it just handles 512 byte sectors
> because of a lack of checking for buffer overruns, and it just happens
> that the 256 byte overrun can be harmless.
> 
> 
> While I have not had time to pursue this further, it means that the
> following is doable:
> 
> 1. A program could be written on a PC or any other platform that
> supports 512 byte sector double density floppies to write the sectors on
> a double density disk so that the COCO could read them.  As the number
> of sectors on the disk get cut in half, it may have to mark them as
> unavailable in the gran table.  The program also has to realize that the
> COCO Basic program will only look at the first 256 bytes in the sector.
> 
> 2. A program on the COCO could be written to read and write MS-DOS FAT
> formatted double density floppies.  It may even be possible to write
> such a program in Extended Color Disk Basic.
> 
> So the question is:  Who will be the first person to write a DISK Basic
> program to display the root directory of an MS-DOS formatted floppy.
> 
> A standard PC Hi-Density 3.5 inch drive will work just fine on the COCO
> if you give it double density media.

I have encountered a drive that flat would not do a thing with DD media 
hooked to a coco3 running nitros9, I assume because it could not deal with 
250 kilobaud data rates even with DD media in it.  Plug that drive in on 
this mobo where it would be getting 500k or even 1 megabaud data rates and 
it was fine.  But only 512 byte sectors on this motherboard.

So I wound up, before DW4, sending whole nitros9 .dsk files to my coco 
using minicom & rzsz, then wrote a dd like utility on the coco to write 
those files to a floppy on the coco.

But then nitros9 came to the rescue again.  I have plenty of space on a 1Gb 
HD on the coco, so a bit of tom-foolery with the /S0 descriptor setting up 
its partition offsets and such, I was able to treat the file on the HD as 
written by rzsz, as a floppy image that I could then access via a cd and a 
dsave, and made the .dsk install without the file going anywhere near a 
floppy disk.  A bit of detective work to setup, but 20x faster than a 
floppy disk being used as a sneaker net medium.

Now, with DW4, I can directly mount the image.dsk and use it exactly as a 
floppy, but again, noticeably faster.

> It also means that such programs could be written for OS-9/NITROS-09 and
> Flex-09.
> 
> Regards,
> -John
> wb8tyw (at) qsl.network
> Personal Opinion Only
> 
> 
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> Coco at maltedmedia.com
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Cheers, Gene
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