The operating system is saved only in 1 Hard Disk Drive unless you create a RAID volume. From BIOS the computer shows you which SATA port is using each Hard Disk Drive. Intel recommends to connect the Hard Disk Drive with the operating system to SATA port 0 always.
BIOS tells you which SATA port contains the hard disk drive with the operating system.
mike_intel is right.
You can set the disk to boot from any SATA port connection: PORT0 ..., SATA:PORT1: ... SATA:PORT2: ... SATA:PORT3 ...
It is not necessary to use the extended drive name.