UNIBUS boot ROMs

DEC produced several generations of UNIBUS ROM boot cards.

• The first was the BM792 ROM quad card, which plugged into an SPC slot; it used individual diodes in an array to represent individual bits, and contained only 32 words of memory.

• The second was the BM873 ROM, also a quad card used in an SPC slot; it contains 128 words, using 2 PROM chips.

• The third was the M9301 ROM card, a dual card intended for use in the top two rows of a MUD slot; it had a capacity of 512 words, using four chips like those in the BM873.

• The last was the M9312 ROM card, which also had a capacity of 512 words.

In both of the latter two cards, the entire ROM contents were directly visible on the UNIBUS, not through a window, unlike later, larger QBUS ROM cards.