How does SATA port multiplication work?

"According to this article on tom's hardware:

The spec allows a maximum of 15 devices per SATA connection
The SATA controller and the port multiplier have to play nice together, which is not a given and usually works only with dedicated SATA controllers. The post you linked to also says that the onboard controller didn't work well with the port multipliers.
No daisy-chaining - the port multiplier does not dupe the controller into believing it's only one drive.
Of course it impacts performance: the drives have to share the connection's bandwidth. If you hook up 10 drives via a 300MB/s SATA 2.0 connection, that leaves only about 30 MB/s to each drives, which is about a third of what a modern drive could supply. Of course that is only relevant when the drives are actually all doing sequential reads at the same time."