With PVM 3.3, it is possible to send and receive messages in a single step using pvm_psend() and pvm_precv(). The messages processed by these routines must be exchanged between hosts of compatible data format. Moreover, since there is no packing, the data sent must be contiguous in the sender memory space. In other words, pvm_psend() can be used to send one array of a given data type to one destination, which is a very common type of message in a parallel application. Nevertheless, this feature cannot be used between hosts with incompatible data format, because it involves no data encoding.