Termination of the SCSI bus is very important but not difficult.
The SCSI bus must be terminated on both ends, but NEVER somewhere in the middle of the bus (cable), so that data can be transmitted to and from all devices without getting reflections on the bus. This means that the SCSI adapter (begin of bus) and the device at the end of the SCSI-cable must be terminated. Terminators are special electrical resistors. With some devices you have to manually insert or remove this terminator. Other devices have built-in terminators that can be enabled or disabled via switches or software commands. 

Termination on your Plextor CD-ROM Drive : Below you can find the settings for internal and external drives of the current Plextor models. For previous models please refer to the manual that comes with the CD-ROM drive. 

Internal Drives External Drives 
  

On host adapters the termination is usually enabled by default. You don't have to change the termination if you use only internal SCSI devices or only external SCSI devices. With most Adaptec host adapters you don't even need to be concerned about SCSI termination, since many boards automatically adjust their termination for different configurations. However, always check the adapters manual when connecting both internal and external SCSI devices!

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