BA11-S mounting box
Since it was a Q/CD backplane, dual-width QBUS cards could only be placed in the left-hand slots, and quad QBUS-only cards had to not use any pins on the right-hand C/D connectors. (The only DEC card with a problem with this seems to have been the MMV11-A.)
It was available both with a front panel with a bezel (with 'Boot', 'Halt' and 'LTC On' switches, and power and run status indicators); and also with a blank front panel (for use as an expansion box).
It was a 5-1/4" tall mounting box, for the H960 series of 19"-wide racks, one of the BA11 mounting boxes. The H960 racks provided 63" of vertical mounting space, divided into units of 10-1/2", which were further subdividable into a pair of 5-1/4" spaces. The 5-1/4" tall BA11-S mounting box was designed for these spaces.
For rack mounting purposes. it did not use external slides (as all the other BA11 mounting boxes did); instead, it was housed in an external 'skin' (termed a 'logic box cover' in DEC documentation, the base unit being called a 'logic box') into which it is slid; the cover would be bolted to the rack.
The backplane was mounted vertically, facing backward (unlike the BA11-M mounting box, where they had been facing forward). Cooling fans mounted on the side of the BA11-S passed air both over the boards, and through the power supply.
The BA11-S's dimensions were 5-1/4" high, 19" wide, and 22-3/4" deep, and it weighed 44 lbs (without any boards). The rack mounting was 26-3/4" long.
- PDP-11/23B Mounting Box Technical Manual (EK-23BMB-TM-001) - not available online