[Coco] Disk Basic and 512 byte block floppies.

[John E. Malmberg]

After reading about how the IDE was supported on HGB dos, I decided to 
try an experiment with ROM BASIC on a COCO II.

I formatted a 720K 3.5 inch floppy with 512 byte sectors on OpenVMS 
because ODS-2 puts some readable ASCII in the first sector.


I then put the floppy in the Color Computer, and used the DSKI$ command 
to read the first sector.  The CLEAR 520 command is needed to reserve 
enough string space.

The text string "OPENVMS      is not a system disk" was clearly 
displayed on the Color Computer.

I then did A$="HELLO FROM COLOR COMPUTER", and used the DSKO$ command to 
write it to the disk.

Placing the Floppy back in the OpenVMS system and examing the first 
block resulted in me seeing the same text.

So it appears that it should not be too hard to patch DISK basic to deal 
with 720K 512 byte blocked media.  Either simply using them at 1/2 
capacity, or remaping the sectors beyond 9 to the other side or to 
tracks beyond 35.

Clearly more experiments are in order, but if a standard method of 
remaping the sectors were developed, it would allow emulators on most 
platforms to directly interchange floppies with the Color computer.

At the minimum, it appears that I can use a BASIC program to write on 
floppies that are readable on OpenVMS in a RAW form.  Which means it 
will easily work on LINUX/UNIX also.

There is documentation on the wild wild web for Microsoft Windows to 
directly read and write to 512 byte media also.

-John
wb8tyw at qsl.network
Personal Opinion Only


EAGLE> init/dens=dd dva0:
_Label: OpenVMS

EAGLE> MOUNT/FOR DVA0:
%MOUNT-I-MOUNTED, OPENVMS mounted on _EAGLE$DVA0:

EAGLE> DUMP DVA0:/BLOCK=(START:0,COUNT:1)

Dump of device DVA0: on 16-JAN-2004 17:01:46.09

Logical block number 0 (00000000), 512 (0200) bytes

  03039401 001E65C0 11C00200 15C600A0 ..Æ...À.Àe...... 000000
  8BDFFF76 905F0000 000501FB 000609F7 ÷...û....._.v.ß. 000010
  20202053 4D564E45 504F0087 80FDFF74 t.ý...OPENVMS    000020
  73206120 746F6E20 73692020 20202020       is not a s 000030
  0000000A 0A0D6B73 6964206D 65747379 ystem disk...... 000040
EAGLE> DISM DVA0:

Disk removed and placed in Color Computer and then returned.


EAGLE> MOUNT/FOR DVA0:
%MOUNT-I-MOUNTED, OPENVMS mounted on _EAGLE$DVA0:

EAGLE> DUMP DVA0:/BLOCK=(START:0,COUNT:1)
Dump of device DVA0: on 16-JAN-2004 17:15:20.50

Logical block number 0 (00000000), 512 (0200) bytes

  524F4C4F 43204D4F 5246204F 4C4C4548 HELLO FROM COLOR 000000
  00000000 00000052 45545550 4D4F4320  COMPUTER....... 000010
  00000000 00000000 00000000 00000000 ................ 000020