For simple single-part messages, the OS provides functions that take a pointer directly to a buffer without the need for an IOV (input/output vector). In this case, the number of parts is replaced by the size of the message directly pointed to.
In the case of the message send primitive—which takes a send and a reply buffer—this introduces four variations:
|Function||Send message||Reply message|
The other messaging primitives that take a direct message simply drop the trailing v in their names: