The PDP-15 was an 18-bit minicomputer by Digital Equipment Corporation that first shipped in February 1970. It was the fifth and last of DEC's 18-bit machines, a series that had started in December 1959 with the PDP-1. More than 400 were ordered within the first eight months. A later model, the PDP-15/76, was bundled with a complete PDP-11, allowing the PDP-15 to use peripherals for the PDP-11's popular Unibus system. The last PDP-15 was produced in 1979, with total sales of about 790 units.
The PDP-15 was essentially a version of the earlier PDP-9 that was constructed using small-scale integration integrated circuits, which made it smaller and less expensive than the PDP-9's flip chips which used individual transistors. A basic 8 kW PDP-9 cost about $35,000 in 1968 (equivalent to $316,000 in 2024), whereas the PDP-15 with 4 kW was only $15,600 (equivalent to $126,000 in 2024) and a fully-equipped system with 8 kW, punch tape, KSR-35 terminal, math coprocessor and dual DECtape was $36,000 (equivalent to $291,000 in 2024), making a complete system significantly less expensive than the earlier machine.