The pvmd and libpvm use the same message header, shown in Figure . Code contains an integer tag (message type). Libpvm uses Encoding to pass the encoding style of the message, as it can pack in different formats. The pvmd always sets Encoding (and requires that it be set) to 1 (foo), Pvmds use the Wait Context field to pass the wait id's (if any, zero if none) of the waitc associated with the message. Certain tasks (resource manager, tasker, hoster) also use wait id's. The Checksum field is reserved for future use. Messages are sent in one or more fragments, each with its own fragment header (described below). The message header is at the beginning of the first fragment.
Figure: Message header