[Simh] More than 4 Drives ?

[Tim Shoppa]

> Seems that simh is limiting me to having a maximum of 4 drives,
> rq0 to rq3.  When I try and define an rq4 I get a "Unit disabled" error".

True DEC MSCP controllers only supported up to 4 drives per controller.

The MSCP protocol allows more than 4.  And there's some OS support (RT-11,
RSX-11 with a patched SYSGEN, VMS out of the box) if you have a controller
with more than 4 drives.

I think if you rebuild simh with RQ_NUMDR (in module pdp11_rq.c) set to
a number bigger than 4 it oughta work just as the real hardware.

There were non-DEC MSCP controllers that did allow more than 4 MSCP
drives.  e.g. CMD 440, Sigma/Webster WQESD, etc.

Tim.