Memory Expansion Hardware for PDP11 Computers

We have developed two hardware methods to expand the data storage region of any UNIBUS PDP-11 program needing rapid random access to large data areas. The first, known as a "Bus Mirror", is a modified DEC DR-11-B (DECKit 11-D) wired to allow program controlled modification of any location on the PDP11's UNIBUS. It performs the reads and writes in a DMA mode, and does not require use of DEC's slow PLAS system directives. The second, known as "Dataspace Memory", is a modified Plessey memory board operating like the "Bus Mirror". It provides 64 kwords of additional storage on the UNIBUS, but invisible to the normal UNIBUS addressing scheme. This has given us a PDP 11/60 with 188 kwords of memory, with a design limit of 33 megawords.