UNIBUS boot ROMs

DEC produced several 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 another early quad ROM card, the M873, but almost next to nothing is currently known about it; apparently it contains 128 words, using 2 of the ROM chips like those in the M9301.