一個 SATA 頭連接多過一部嘅 SATA 硬碟........?

you are half right...

its eSATA(e=external) which allow up to 15 devices to connect using one channel, with a port multiplier.

and there are SAS, Serial attached SCSI, which allow up to 4 devices on one channel.

or..PATA, parellel-ATA, which obviously from its name, allows 2 devices on one channel(hence parellel to each other)

BUT not the SATA, not even the SATA 150 or SATA 300...they are still running one device per line