|It is reserved for IDE devices. Evidently you don't have any IDE devices installed.|
I ask again, why do you care? The only reason the listiings are like they are is because BIOS setting change comes slow. Eventually there will be separate listings for SATA drvies. Right now most SATA devices are being run in an IDE compatibility mode. Eventually that will change.
FYI, all SATA devices are in essence Masters. The SATA controller has TWO ports. In order to label those two ports Master and Slave designations are used. Both run independently though at full speed and don't need to share the bandwidth.