SCSI hard drives are generally more expensive than IDE drives due to their faster data transmission rates, despite having similar capacities and RPMs. SCSI technology allows for greater flexibility, supporting up to 15 drives in a system compared to the 4-device limit of IDE, which is particularly beneficial in server and graphic workstation environments. Additionally, SCSI drives often include RAID capabilities, enhancing data redundancy and performance. While IDE drives can also implement RAID configurations, SCSI's design allows for hot-swapping, enabling users to replace failed drives without shutting down the system, minimizing data loss. SCSI typically requires an additional adapter card, as most motherboards do not natively support it, except in server setups. Overall, SCSI's advantages in speed, flexibility, and reliability contribute to its higher cost compared to IDE drives.