scsi component

Scenario 1 is common in desktop computers where you connect a single device to a single adapter and perform data transfers. There is practically no difference between the two interfaces, this holds for bandwidth as well as resource usage as both interfaces use the most efficient way to transfer data, namely DMA. There is no point in purchasing a generally speaking more expensive SCSI based system when the cheaper ATA interface. Scenario 2 is common in high-end desktops and servers where you connect multiple devices to one or more interface adapters. This is where SCSI has major advantages compared to ATA. ATA interface can only address 2 devices while SCSI can address 8 devices Narrow SCSI, 16 devices Wide SCSI, 32 Very Wide SCSI or 126 FireWire. The demand for high transfer rates in servers can not be met using current ATA interfaces based on the two devices per adapter limit and even if it could there simply isn't enough bandwidth and flexibility available for server application. ATA devices lack the intelligence to perform command queuing. SCSI which can queue up to 256 commands per logical unit. SCSI hard disk drives aimed at the extreme performance server market have had a lot of research and development time on optimizing seek patterns and rescheduling commands to minimize seek times and maximize throughput. This may not be evident by looking at desktop benchmarks but under heavy server loads, this is evident. Also, SCSI hard disk drives generally tend to be designed to work well in RAID-systems where I/O load is spread across multiple drives. Most high-end SCSI hard drives are quite expensive but there are good reasons for it. They can sustain higher temperatures and stay mechanically functional despite the expansion of the metal parts with temperature and and generelly have better build quality. The net result is that they are the natural choice for enterprise server applications.