[Coco] DriveWire

[Robert Gault]

Boisy Pitre wrote:
> 
> On Mar 5, 2009, at 9:33 PM, Ryan Pritchard wrote:
> 
><snip>
>> Now where I get lost is that with DriveWire 2 you indicate I could boot
>> strap NitrOS-9 from a DriveWire virtual drive.  Isn't the NitrOS-9 
>> Level 1
>> boot diskette either 2 5.25" disks or 1 3.5" disk, since you only include
>> one disk image for NitrOS-9 I presume you are loading the larger disk 
>> image.
>> Does NitroOS-9 support for DriveWire allow for larger disk images?  
>> whereby
>> the virtual drives look like larger Hard Drives?
> 
> Yes, that is correct. Under NitrOS-9, you can format a DriveWire disk as 
> large as RBF will allow (4GB)
> 
 ><snip>

Ryan, I'm not so sure that Boisy answered your question completely.

NitrOS-9 has a module in the kernel on track 34 called Boot. This module 
is by default hard coded to read floppies. If you want to boot from a 
real hard drive via a scsi or ide interface or from a virtual hard drive 
via DriveWire, the boot module must be replaced with a special one to 
access the correct hardware. This is done for you (I think) by Cloud-9 
when you purchase their products.
The size of the drive where the main NitrOS-9 system is installed, is 
not dependent on the interface that talks to the drive as much as it 
depends on the actual OS-9 / NitrOS-9 software. The size of a disk is 
stored on the disk's first sector in 3 bytes indicating total sectors, 
DD.TOT. So you are limited to $FFFFFF sectors. The sectors don't need to 
be 256 bytes (standard) but that is still 4GB.

So when booting via DriveWire or an IDE or SCSI system, you will still 
use a floppy. The floppy can be a virtual floppy in which case it is a 
35 track single sided image containing only the kernel on T17 and the 
os9Boot file.
You can get a feel for this with several emulators using RGBDOS for 
emulators. Both the emulator version of RGBDOS and HDBDOS derive from 
the same RGBDOS sold with KEN-TON SCSI hard drive systems for the Coco.