SCSI devices can be difficult to configure for many reasons. A SCSI adapter card is required for SCSI devices. The SCSI adapter needs a free IRQ to work properly and may fail to work and cause system lock ups if not configured properly. Another problem with SCSI is that the devices have to be terminated properly and each device must have a unique ID number. For the novice, this can be intimidating.
Parallel devices are easier to install but the performance is much slower.
Most computers come with only one parallel connector, so if you have a printer or other parallel device you have to operate off of a pass-through. Unfortunately, many parallel devices do not work properly with pass-through. USB solves these problems. USB comes built into most new computers and operates at a faster speed than parallel. With USB you simply plug in the device and install the driver.