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+Mach ports are [[capabilities]].
+
+A Mach port is a kernel queue. Each port has associated with
+it a receive right and one or more send and send-once rights.
+A queue can hold a number of messages. Once the queue is full,
+the send blocks until their is space to enqueue the message
+(this is interruptible via a timeout mechanism).
+
+A receive right designates a queue and authorizes the holder to
+dequeue messages from the queue, and to create send and send-once
+rights.
+
+Send and send-once rights designate a queue and authorize the
+hold to enqueue messages (in the case of a send-once right,
+a single message). Enqueuing a message is equivalent to
+[[invoke|invoking]] a capability.
+
+Send and receive rights are named using local names. Each
+task has associated with it a port address space. A ports
+are addressed via this table. Each task thus has its own
+private [[NamingContext]] for ports.
+
+Ports can be [[delegate]]d in an IPC message. When the
+receiver dequeues the message, the right is made available
+to it.
+
+A thread can only block receiving on a single port. To work
+around this, the concept of a port set was introduced. A receive
+right can be added to (at most) one port set. When a thread
+receives from a port set, it dequeues from any of the ports that
+has a message available. \ No newline at end of file