UNIBUS boot ROMs

DEC produced three generations of UNIBUS ROM boot cards.

The first was the BM792 ROM card, which used individual diodes in an array to represent individual bits; it contained only 32 words of memory. The second was the M9301 ROM card; it had a capacity of 512 words, using PROM chips. The third 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.

There was also a specialized card for use in the PDP-11/40 machines, the M793-YA.