The abstraction of a computer system as a set of asynchronous communicating processes is an important system concept. This paper indicates how the concept could be supported at a low hardware level. A new inter-process communication mechanism called a mailbox is introduced. Examples of its use as a programming tool are given. This is followed by a description of hardware features that use this mechanism as the basis of communication between the components of a complete system. These features include processor-sharing hardware capable of handling process selection and switching with high efficiency. It is also indicated how these features can take the place of conventional input/output structures.