Yes, you can it's backward compatible.
SATA 3 is backwards compatible, it means you connect it the same way as SATA 1.
Internal CD ROMs and DVD ROMs plug into either SATA, ATA (PATA), or SCSI sockets. External drives plug into USB, E-SATA, or Firewire sockets.
SATA hard drives are hot swappable, meaning that you can can unplug it while the computer is on just like a flash disk. Make sure that the power is already connected, it is not recommended to plug in the power connector while the machine is powered on. The SATA data cable is plug and play.
Speed of sata 1 is 1.5 Gbps Speed of sata 2 is 3 Gbps
Ø SATA I- 1.5 Gb/sec, SATA II- 3 Gb/sec and SATA III- 6 Gb/sec
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.
No Master Slave designation needed. SATA Drives are plug-add-play. Improve: SATA (Serial) Attached Drives improve data tansfer speeds up to 10-100 GBytes/per. eSATA are (Externally) Serial-Attached Drives and SATA-II(Sata-2) Drives transfer data @ 300GBytes/per. The next barrier of TerraByte data transfer has been developed and is already in production with a (SATA-3) designation attached
Serial ATA is a type of hard drive connector and standard. Instead of a 40-pin parallel ATA plug, is uses around 6 wires to send the data in a serial fashion. If you don't have SATA sockets or not enough for your needs, then you have to install an expansion card with SATA connectors. They are available for different types of expansion sockets, support different SATA standards (generation 3 is the current standard), and have different numbers of SATA sockets.
Ø SATA I- 1.5 Gb/sec, SATA II- 3 Gb/sec and SATA III- 6 Gb/sec
Well... First, you have to plug it in..
If you plug a SATA 3.0 drive into a SATA 1.5 port on your motherboard, the drive should be able to function at a 1.5Gb/s transfer rate. Some drives require a jumper setting, while others natively recognize their allocated bandwidth and adjust accordingly.
How is the backup drive connedted to the computer? If it is connected by USB, the rectangular plug, then it might take an hour or more. If it is connected by a SATA plug, which looks like a USB, except it is shaped slightly less like a rectangle, it would take significantly shorter time, though I don't know how much shorter, since there is SATA 6 and SATA 3, which both affect the required time. 120 Gb is a lot to back up, so don't expect it to go quickly.