Scuzzy Termation Question

ricktea

I've been reading Mike Meyers Passport book, and
there is one question, I am confused about.

"How would you terminate a SCSI system, that has
1 Internal Hard drive and 1 External Cdrom drive
connected to the host adaptor.

A. Terminate the Hard drive and Cdrom drive
B. Terminate Hard drive, cdrom, and host adaptor.

The correct answer given was A.
I am confused, because I read you must always
terminate the host adaptor. If the host adaptor
plugs into the motherboard, its on the end so
shouldn't it be terminated also, since they always
say in the book you must, terminate both ends.
Sometimes they say "always terminate the end of a scuzzy
chain, and sometimes they say "always terminate "both" end
of a scuzzy chain. I've never worked with scuzzy, I can't
figure this out, can someone simplify this for me. thanks

oldtech

Terminate both ends of a chain wether one end is internal or not. The host adapter would not be the end as it has an internal device attached to it.. Terminate just the host adaptor if that is the last device in the chain, if it was every device would be external so terminate last external device and the host adapter e.g both ends of the chain.
Heres the link to technotes scsi notes
http://www.techexams.net/technotes/scsi.shtml

ricktea

thanks, but I'm not sure I undersand.

You mean in this case where there is 1 external cdrom, and one internal hardrive,,, then the host adaptor would be like in the
middle, so it would not be terminated. Is this right .

Also, perhaps if there was just one external cable,,would you
then have to terminate both the cdrom, and the host adaptor.

Or if there was just 1 internal device, would you then have to terminate the hardrive and host adaptor ? thanks again,,

TheShadow

The rule is terminate end to end just like tying up a clothes line or hammock; i.e. the terminators are the knots. If you have both external and internal devices the adapter is in the middle and its termination is off. If only internal devices or only external devices then the adapter is one of the ends and needs termination turned on. Although I don't think it matters for the test, be aware that some adapters allow two internal cables which then places the adapter in the middle again without termination. The caveat is that if you use both internal cables then no external cable is allowed. From a heavy user of SCSI for ~20 years.