> on my 4000/60 I have a dka300 500MB disk internal
> the scsi host adapter is ID 6
> 
> I Attached an external SCSI CDROM which is a Yamaha CDRW 
> 
> the station does not see it
> 
> with show dev I can only see the net interface, the internal disc and the
> scsi host adapter  ICannot see the cdrom
> 
> on a 4000/90 instead this cdrom was seen.
> 
> also on other 4000/60 station I Cannot see this cdrom external device.
> 
> Could it be because the internal disk terminates the SCSI chain ??

No (the SCSI bus *should* be terminated at both ends).  Maybe the CD-RW
is using the same SCSI ID as another device (causing a conflict).