[Coco] Read coco disks on a PC

[John E. Malmberg]

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.

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

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.

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.

It also means that such programs could be written for OS-9/NITROS-09 and 
Flex-09.

Regards,
-John
wb8tyw (at) qsl.network
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