• Passive – This is basically a bunch of resistors. It does the job, but higher performance drives can’t use it and it only works on distances of 2 or 3 feet. This is used for basic SCSI setups that operate at the standard clock speed of 5 MHz.


• Active – This terminator has a voltage regulator that ensure the correct termination voltage. Many have a LED showing the termination level. This type of termination is used on Fast SCSI systems or systems with more than 3 feet between the controller and the device.

In SCSI setups in which the controller sits in the middle of the chain (it can sit on any position in the chain), then termination muct be provided on both ends of the chain. Where the controller is at one end of the chain, it can serve as termination on that end.

There are a variety of different cable types used, depending on the type of SCSI being used. They are:

Configuration

SCSI drives aren’t that hard to configure. Each device must have a SCSI ID. On SCSI setups supporting 8 devices, the devices are labeled with IDs 0-7. The host adapter takes one ID, usually the highest one. Most adapters are usually factory-set to ID 7, which is the highest-priority ID. Many adapters require that any SCSI boot drive be configured to a certain ID. With the newer ones, it doesn’t usually matter. The ID is configured by some type of switch or jumper on the drive, much like the master-slave jumper on an IDE setup. There are three jumpers used to describe the SCSI ID. Instead of making this simple, manufacturers decided to make the ID # a result of a binary representation of the jumpers. For example, setting all three jumpers off gives a binary of 000, meaning SCSI ID 0. Below is a table of jumper settings:

Depending on the manufacturer, the order of these jumpers may have been reversed. In this case, just flip the order of the jumper settings around. For example, ID 4 above is on-off-off. On a reversed setup, it would be off-off-on. As always, use the manual as the primary reference for these settings. Many drives do not require you to set the ID number manually, instead using plug-and-play technology to assign an available ID automatically.

SCSI in Use

SCSI is nowhere near as popular as IDE. For one, SCSI costs more to setup than IDE. Secondly, it is more involved to get running, especially when you consider the fact that IDE controllers are part-and-parcel of every motherboard on the market, whereas SCSI support built-in to a board is more of an extra. IDE devices, too, are gaining speed on SCSI, so raw speed between the two interfaces is not as large an issue as it once was. When it comes to external devices, USB and Firewire have both marginalized SCSI as an interface. USB 1.1 has more than enough bandwidth potential for most devices, and USB 2.0 and Firewire take the slack for devices requiring higher bandiwdths. USB 2 and Firewire both provide more bandwidth potential than SCSI. SCSI is great in multi-tasking environments because the bus operates independently of the CPU, but for external devices, both USB and Firewire have abilities to operate independently.