One.
SATA interfaces are USUALLY only one device at a time. It is possible, if the controller supports it, to use a port multiplier which allows you to use four devices off one port .
Normally, only one SATA per channel can be hooked up to a motherboard. However, you can buy SATA port multipliers (similar to USB hubs) allowing you to put as many as fifteen devices on a channel. see here: http://www.tomshardware.com/reviews/silicon-image-brings-virtualization-esata,1610-3.html
The easiest way, is to purchase a SATA PCI card. Install this card inside the pc, and it will allow x amount of extra sata devices, depending on how many the card will support. Hope this helps
Generally speaking, only one. However, there are some devices, known as "port multipliers" that will allow you to connect up to 15 devices to a single channel.
Four computers and two phone devices can be connected with that.
Yes. You can add as many hard drives, or other sata devices (DVD burners etc) as will fit into your case, or until you have no more sata connectors free.
2 devices
2
Traditionally, it has been PATA (IDE), but many newer computers are using SATA DVD drives.
I read by 2012, 17 billion devices will be connected to the internet
SATA is ATA, but there are many ATA. SATA is an acronym for Serial AT Attachment, AT being the successor to the PC standard of desktop computers. There are many ATA standards, lots, but short answer is they are outdated Paralel, so we coined a new term to cover all the old ATA devices: PATA.
16 devices can be connected
The number of devices you can link to a router will depend on the specific router,typically 4 devices can be connected.