SCSI or Small Computer Serial Interface - was used in servers for a long time because of the a few reasons - once was the number of drives that could be handled (up to 7 per chain) - often capacity and RPM was higher than IDE drives as well - however, in recent years, IDE has caught up to SCSI in regard to capacity, transfer rate and RPM so the difference is much less. The biggest reason SCSI was used for servers however was not any of the reasons mentioned so far, but it's ability to stack access commands. SCSI interface can buffer disk requests from multiple users on a server and prioritize the requests based upon their position on the drive for more efficent access making them ideal for server based applications. With a single user PC - this advantage is unnecessary and with the higher costs involved with SCSI and the need for a seperate interface, SCSI was not the choice for user PC's
Firewire or IEEE 1394 (originally at 400 M/s) is much faster than USB 1 (1 M/s) and USB 2 (480 M/s) may beat it, but an 800 M/s version of firewire is now available. SCSI's Ultra320 is now the fastest interface for that side, but SATA actually performs better even at 150 M/s. Considering the internal IDE max out at 133 M/s, firewire externals may appear to give good competition against internal HD's. This is not the case however. In looking over some benchmarks from
Tom's Hardware it would appear that the max transfer rate is a dismal 40 M/s or less. Despite the high interface transfer rate, performance of external drives just don't hold up compared to internal systems which achieve up to 150 M/s (see this article at
Tom's )
So stick with a nice fast internal HD with SATA if possible for the fastest performance. If you really want speed, go with a raid array, but external's are not a good choice for this application.