BM792 ROM

The BM792 ROM card was a UNIBUS card for the PDP-11 series of computers; it was a quad format card, and contained only 32 words of memory. Most versions were used for bootstrapping the machine, from disk, paper and magnetic tape, etc, but it could be use for any purpose

It used individual diodes in an array to represent individual bits; if the diode was present, the bit contained a '1'; if the diode was not present, a '0'. Jumpers allowed the board to occupy any 32-word block from 773000 to 773700, so longer programs could be accomodated with multiple cards.

The board came in two main variants: the BM792 came fully populated with diodes, and the user removed diodes (either by desoldering them, or clipping their leads) to produce the desired program; other variants, designated BM792-Yx (where 'x' is a capital letter, starting with 'A') came pre-programmed from DEC to perform various functions.

Variants

• BM792-YA - Serial line, high-speed paper tape reader
• BM792-YB - TC11 DECtape and disks (RC11, RF11, RK11, RP11)
• BM792-YC - Card reader
• MR11-DB - A two board set, consisting of the BM792-YD and -YE, it supported the same devices as the -YB, with the addition of the TM11 magnetic tape
• BM792-YF - DECtape and RF11 and RK11 disks
• BM792-YH - TA11 casette magnetic tape

See also

• UNIBUS boot ROMs

Reference

• DEC-11-HBMAA-E-D, BM792 read-only-memory and MR11-DB bootstrap loader