Avoid the use of operating system and language features that would be hard to retrofit if unavailable to ensure portablitly. PVM does not use multithreading or asynchronous I/O.

Message Model
Arbitrary length messages
Typed data
XDR (eXchange Data Representation) used between hosts with incompatible data formats.
Senders do not wait for acknologment

Fault Dectection and Recovery
Recover from the loss of any pvmd, except the master
Slaves disconnected fromt the master shutdown to prevent partitioning
Virtual machine halts if the master crashes or is disconnected

Resource Manager
Advanced task and host scheduling

Protocols
pvmd-pvmd : N to N UDP with PVM managing reliable transport and fragmentation
pvmd-task and task-task : 1 to 1 TCP