Fastest Sata Hdd Are SATA HDD's And A SATA II HDD's Interchangeable On SATA II Supported Mobo's?

Are SATA HDD's and a SATA II HDD's interchangeable on SATA II supported mobo's? - fastest sata hdd

I was told, SATA II hard drive is twice as fast as the first generation of SATA HDD, is this true?

A hard disk SATA (not SATA II) on the motherboard for the work of the following?

PATA 2 x ATA100 up to 4 devices
SATA 3Gb / s 5 x SATA II
1 x SATA II on the back
RAID SATA RAID 0/1/0 +1 / 5
Additional RAID Controller Sil 3132

And why do we need RAID? How do you use and why should we use?