IDE drives require only a simple connection inside the computer. Until recently, the major drawback of IDE drives was a limit of two hard disks per machine. But newer IDE interfaces can handle up to four hard drives. Most new computers have the IDE adapter built right onto the main circuit board. Macintosh computers and some heavy-duty PCs use SCSI drives.
SCSI drives require a sophisticated controller board inside the computer.
SCSI's main advantage is that one controller can handle up to seven hard drives or other devices, like scanners or CD-ROM drives. The faster your hard drive, the better your computer will perform.