All patents covering the PDP-11 architecture are expired by now. The PDP-11 is completely unencumbered from an intellectual property point of view since 1995. But it's quite interesting to look through the patents. They are now easily accessible via Google Patents. The key PDP-11 architecture patents are:
- US-Pat 3614740 (1971) - covers PDP-11 Instruction Set (control transfer)
- US-Pat 3614741 (1971) - covers PDP-11 Instruction Set (PC as general register)
- US-Pat 3710324 (1973) - covers 'processor and peripheral connected via single bus' UNIBUS architecture
Other PDP-11 and UNIBUS related patents are:
- US-Pat 3376554 (1968) - covers PDP-6 architecture; by Alan Kotok and Gordon Bell; cited in several PDP-11 patents
- US-Pat 3675083 (1972) - covers physical implementation of UNIBUS
- US-Pat 3670311 (1973) - covers serial interface to switch and display console
- US-Pat 3854126 (1974) - covers PDP-11 memory management and address room extension
- US-Pat 3815099 (1974) - Division of US-Pat 3710324 (PDP+UNIBUS)
- US-Pat 3940743 (1976) - covers UNIBUS windows (bus windows)
- US-Pat 3999163 (1976) - covers MASSBUS
- US-Pat 4030073 (1977) - covers power-on reset and boot logic
- US-Pat 4047157 (1977) - covers dual-ported MASSBUS devices
- US-Pat 4055851 (1977) - covers PDP-11/70 cache system
Design patents covered the visual appearance (uspto term: ornamental design) of the PDP-11 systems and peripherals, for example
- US-Pat D229830 (1974) - covers switch + display front panel
- US-Pat D244034 (1977) - covers VT52 like video terminal
- US-Pat D249512 (1977) - covers PDP-11 like system console and rack
- US-Pat D254371 (1978) - covers RK06 disk + 11/60 CPU style cabinets
The trademarks PDP, UNIBUS, MASSBUS, DEC, and DIGITAL ( d|i|g|i|t|a|l ) are all marked as dead and are thus expired, the last one in April 2010.
