The CADR microprocessor is a general purpose processor designed for convenient emulation of complex order codes, particularly those involving stacks and pointer manipulation. It is the central processor in the LISP machine project, where it interprets the bit-efficient 16-bit order code produced by the LISP machine compiler. (The terms “LISP machine” and “CADR machine” are sometimes confused. In this document, the CADR machine is a particular design of microprocessor, while the LISP machine is the CADR machine plus the microcode which interprets the LISP machine order code.)