IDE and SCSI are two differen interfaces to connect hardware to the system board.
SATA (serial ATA) drives allows for greater data transfer rates.
They can also be used for creating larger faster storage spaces when included in arrays. These drives are usualy a bit more quite and are dearer then their PATA (Parallel) counter parts. These will connect to the bord via a SCSI interface.
ATA drives are more common as they connect to the board via an IDE interface and most common motherboards have got IDE sockets in them.
Not all motherboards support SATA. These drives will be more afordable.
If you are building a system from scratch you can conceder SATA technology. However, if you already have a comoputer and you wish to upgrade, you need to acertain whether you system supports SATA.
Good makes - Western Digital, Seagate, Samsung, Fujitsu to name a few.