message queueing questions?

[Victor L]

Can someone explain how message queueing in partition(s) work?
Specifically:
Is there any buffering before message is committed to log (written to disk) ?
Does the term "partition" refer to sequence of messages written to disk, or
are the messages stored in memory queue and written to disk only after that
memory queue is full? If there's no buffering, can message be lost before
it's committed?
Does the message needs to be committed to the log before it can be
consumed?
Thank you