BA11-C Mounting Box
The BA11-C Mounting Box was one of the two earliest earliest standard system unit backplane mounting boxes produced by DEC, along with the BA11-E Mounting Box. It was used to hold the KA11 CPU and front console (programmer's console or 'controller console') for the PDP-11/20 (hence the -C variant suffix).
It came in two variants, the rack-mounted BA11-CS (including Tilt and Lock chassis slides), and the table-top BA11-CC. The rack-mounted ones were usually mounted in the H960 series of 19"-wide racks, which provided 63" of vertical mounting space, divided into units of 10-1/2". The 10-1/2" tall BA11-C mounting box was designed for these spaces.
The system units were mounted transversely, but because the cooling fans were mounted along the side of the box, they could not hold extended-length hex-height cards; only shorter (lower) modules, such as the M920 UNIBUS Jumper, could be placed in the A-row connectors.
The system units faced downward (unlike the later BA11 mounting boxes, where they were facing up); the reason was probably to give easier access to the backplane wiring for debugging. The unit could rotate to give easier access to the boards.
The BA11 came with the H720 Power Supply; it was mounted transversely in the box at the rear.
The power harness ran along the left-hand side; it contained a number of single-width stub cards, which plugged into the power supply slot in the system units (generally the A connector in slot 3).
The BA11's dimensions were 10-1/2" high, 19" wide, and 23" deep; the H720 was 8" high, 16-1/2" wide, and 6" deep, and weighed 30 lbs.