Abstract: From the viewpoint of concurrent and distributed programming, several concurrent and distributed programming languages were analyzed and compared. A novel structured distributed and concurrent language Orc was designed and implemented by Professor Jayadev Misra. After analyzing the fundamental principles and languagccharacters,a new concurrent and distributed mechanism of Apla (Abstract Programming LAnguage) was originally designed in the paper. The mechanism includes the concurrent operator, concurrent statements, the definition, communication and synchronization of process. hhe feasibility and practicability of the mechanism were illustrated by giving a representative example. Finally, many advantages (such as generality, simplicity, abstract, easy-to-writing) of the concurrent and distributed mechanism were presented.

Key words: Concurrent and distributed programming, Orc language, Apla language, Concurrent and distributed mochanism