Hewlett-Packard's reduced instruction set computer (RISC) processor architecture. See RISC.

The PA-RISC is a RISC processor developed by Hewlett-Packard. It is currently produced only by HP. At the moment only one OS runs on PA-RISC based machines: HP-UX. There is an effort underway to port Linux to them, though.

HP's Precision RISC Architecture. Also known as HP-PA or PA.