BA11-K mounting box
The BA11-K mounting box was for many years the standard hex system unit backplane mounting box for the H960 series of 19"-wide racks produced by DEC, one of the BA11 mounting boxes. It could contain up to 5 standard size (4-slot) system units.
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 10-1/2" tall BA11-K mounting box was designed for these spaces.
BA11-K's were used in both 'basic box' and 'expansion box' roles. The latter was used to hold extra devices, and had a blank front panel. The former contained the CPU, and had a front panel of some sort - either a programmer's console, or an operator's console.
In the PDP-11/04 and PDP-11/34 (the models which used this mounting box to hold the CPU) the front panels were the KY11-LA Operator's Console and the KY11-LB Programmer's Console (the same for both CPU's).
The system units were mounted longitudinally, facing upward (unlike the BA11 mounting box, where they had been facing down); they were generally mounted with the A-row connectors at the back, next to the power distribution panel.
The BA11-K came with the H765 Power System, which was a separate unit, mounted transversely at the rear of the box; it contained up to four DEC standard modular regulators. The power harness from it ended in a power distribution panel containing standard DEC power distribution connectors.
Cooling fans mounted on the front face of the H765 passed air both over the boards, and then through the power regulators.
The BA11-K's dimensions were 10-1/2" high, 17-1/8" wide, and 17-1/4" deep without the power supply; with the H765 added, it was 26-1/2" deep, and weighed 87 lbs (without any backplanes or boards).
The BA11-K was also used in custom configurations to hold systems such as the MJ11 memory system and MK11 memory system, with a custom backplane and power harness. Technically, these boxes were not BA11-K's, but they share physical hardware, basic power system, etc with the BA11-K.