One is message-passing model and the other is shared-memory model.
Message-passing strengths and weaknesses:message can be exchanged between the processes either directly or indirectly through a common mailbox.it is userful for exchanging smaller amounts of data and easier to implement for intercomputer communication.however,its speed is slower than shared-memory model.
Shared-memory strengths and weaknesses:it allows maxmum speed and convenience of communication.however,in the areas of protection and synchronization between the processes some problems exist.