[Simh] Limits on MSCP controllers

[Bob Supnik]

The four ports is not arbitrary. SimH simulates actual hardware. DEC 
never built a backplane MSCP controller with more than four ports.

If you want to extend the current RQ simulator to include third party 
boards (either SMD-based emulators or SCSI-based emulators), feel free 
to add an appropriate mode switch. I don't know what controller ID these 
third party boards returned, though, nor do I know how VMS determined 
the number of ports per controller.

I think it would be better to understand why VMS is waiting to mount 
additional discs. Alternately, just create bigger discs and have fewer 
of them.

/Bob

On 6/23/2019 12:00 PM, simh-request at trailing-edge.com wrote:
> This is, though, another slight silliness in simh. The limit to 4 disks
> per controller is very artificial. The UDA50, KDA50, and maybe some
> other controllers only have four actual, physical ports, which limited
> them to only have four disks per controller. However, MSCP itself do not
> have such a limitation, and common SCSI controllers for these machines
> which use MSCP allows more than four disks on a controller, and most
> software (at least RSX and VMS) also do not limit themselves to only
> configure max four disks on a controller. I wish simh didn't put such
> arbitrary limitations in. simh also decides on unit numbers by itself,
> which could also have been nice to be able to choose.