> On Dec 11, 2017, at 11:37 AM, Johnny Billquist <b...@softjar.se> wrote:
>
> Paul. The RM06 has its own massbus id. The device can also emulate existing
> dec disks, which means no changes needed. But when identified as an RM06 it
> becomes a bit more interesting as this device does not have a fixed size.
> Similar to mscp in that way. It has fixed numbers for sectors/track and
> tracks/cylinder but the number of cylinders depends on the actual disk. So
> the os must figure disk size out at runtime.
>
> I know rsx does it, as I have the sources. I would expect that Mentec also
> added this for RSTS/E but I have not actually checked that.
I don't know that Mentec did anything to RSTS other than change the logo on the
cover of the manuals.
RSTS handles non-MSCP disks by determining the drive type, then looking up the
geometry in a table. So for Massbus, there's a table that lists Massbus ID
values and the corresponding sector/track/cylinder counts. There isn't any
support for a given ID having varying size.
It certainly would be possible to write code that pokes at a disk to see how
big it is, but RSTS doesn't do that. Well, except for the very unofficial PRO
support I added, which is buried in the V10 code of INIT but not otherwise
exposed. That distinguishes some PRO disk models by doing I/O to check the
size, and/or to see how many heads there are. But for non-Pro PDP11s, RSTS
doesn't do it that way.
Unlike RT or RSX, RSTS was never intended to be customized by users, so there
is no support for user-written drivers or any easy way to handle peripherals
not supplied by DEC. It's certainly possible to do the work if you have the
sources, but neither the process of writing drivers not the way to build an OS
are documented.
paul
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