[Coco] Question regarding OS-9 Default Drive (/DD)

[Robert Gault]

Nick Marentes wrote:
> I am wondering how OS-9 handles the default drive.
>
> I always thought that the idea behind OS-9 is that regardless of your OS-9
> hardware, the driver maps the hardware to a software "translator" (my terms
> because I don't know the official terms yet). This is the default drive (/dd)?
>
> That way, whether you have a 40trk, 80trk, drivewire, SDC etc drive, the
> application program doesn't care because it talks to this "software/device
> translator".
>
> So, what has me wondering is why, when I look at the NitrOS-9 software website
> (http://nitros9.sourceforge.net/latest/) there are so many files and many are
> just duplicates but configured for there respective loading device?
>
> Seems messy, confusing and goes against what I thought was how OS-9 works.
>
> I would have thought that once one configures an NitrOS-9 to suit their setup,
> the single version of the application disk/s is all that is needed.
>
> Does this mean that when a new program is added, a version of the same
> application needs to be created for each device?
>
> Seems wrong and but I'm sure there is something I'm not understanding here.
>
> Nick
>

Nick,

While /DD is the default drive, just what that drive actually is depends on the 
content of the descriptor /DD. Put another way, any disk that is bootable can 
have a /DD in the OS9Boot file but that /DD had better "point" to the disk in 
question. In short, the repository will have different /DDs for each different 
disk type.

An example will probably help. My Ken-Ton hard drive system has a /DD in the 
OS9Boot file but that /DD is for a scsi hard drive. Compare that with /DD from 
one of the 40d disks in the repository which are for 40 track double sided 
floppies. A /DD for Drivewire will be different from the above two.
So why would you even want /DD? Lets say that you write a program that requires 
disk access and you want it to work on both my hard drive and a floppy system. 
You also are not sure what directory a user is currently within. That means you 
need an absolute rather than relative directory path and use /DD/NicksProgram.
The bootable distribution disk being a floppy will run the program because the 
/DD on that disk is a floppy. When I migrate the contents of your disk to my 
hard drive, the program will also work because my /DD is for a hard drive.

Robert