Programmed Data Processor model 11.
A series of minicomputers based on an instruction set designed by C. Gordon Bell at DEC in the early 1970s (late 60s?). The PDP-11 family, which came after, but was not derived from, the PDP-10, was the most successful computer of its time until it was itself succeeded by the VAX.
Models included the 11/23 and 11/24 (based on the F11 chipset); 11/44, 11/04, 11/34, 11/05, 11/10, 11/15, 11/20, 11/35, 11/40, 11/45, 11/70, 11/60 (MSI and SSI); LSI-11/2 and LSI-11 (LSI-11 chipset). In addition there were the 11/8x (J11 chipset) and SBC-11/21 (T11 chip) and then there was compatibility mode in the early VAX processors.
The B and C languages were both used initially to implement Unix on the PDP-11. The microprocessor design tradition owes a heavy debt to the PDP-11 instruction set.
See also SEX.