What are all the differences between pipes and message queues?

Message Queues are:

• UNIDIRECTIONAL
• Fixed number of entries
• Each entry has a maximum size
• All the queue memory (# entries * entry size) allocated at creation
• Datagram-like behavior: reading an entry removes it from the queue. If you don't read the entire data, the rest is lost. For example: send a 20 byte message, but the receiver reads 10 bytes. The remaining 10 bytes are lost.
• Task can only pend on a single queue using msqQReceive (there are ways to change that with alternative API)
• When sending, you will pend if the queue is full (and you don't do NO_WAIT)
• When receiving, you will pend if the queue is empty (and you don't do NO_WAIT)
• Timeouts are supported on receive and send

Pipes

• Are a layer over message Queues <--- Unidirectional!
• Have a maximum number of elements and each element has maximum size
• is NOT A STREAMING INTERFACE. Datagram semantics, just list message Queues
• On read, WILL PEND until there is data to read
• On write, WILL PEND until there is space in the underlying message queue
• Can use select facility to wait on multiple pipes

That's what I can think of right now.

"VxWorks pipes differ significantly from UNIX pipes", says the vxWorks documentation, and they ain't kidding. Here's the manpages.

It looks like it would not be exaggerating much to say that the only similarity between Unix pipes and vxWorks pipes are that they're a form of IPC. The features are different, the APIs are different, and the implementations are surely very different.

I also found this difference in IPC in UNIX. It states that the difference between them is that Message queues and pipes is that the first stores/retrieves info in packets. While pipes do it character by character.

Msg queue:

Message queue: An anonymous data stream similar to the pipe, but storesand retrieves information in packets.

Pipe

Pipe: A two-way data stream interfaced through standard input andoutput and is read character by character

I also found this question here: Pipe vs msg queue