internal scsi termination 50 pin/68pin problem

[Jim Bauer]

On Friday 17 September 2004 22:52, paynito wrote:
> the quantum drive is an internal
> (ultra 3= scsi 2=68 pin)
> while my pmac 9500
> seems built for narrow scsi 1
> the sys original hdd is of course
> terminated and seems to have no option
> to turn off termination
> i.e. i can't take an 8100 hdd
> and daisy chain it inside the 9500

Have you looked up the specs for the drives?  They may have a termination 
jumper that is just not labeled very good.

> are you saying to
> get a 25 pin passive terminator, connect
> it to the outside of my box and this
> will provide termination to a drive on
> the internal scsi chain?

That won't work.  Termination must be at the drive or at the end of the cable.  
Many modern SCSI devices (or maybe more expensive ones) are able to 
auto-terminate themselves.

> it seemed to me like the apple cdrom
> was terminating itself, the apple hdd
> was terminating itself and the external
> hdd was then being terminated by an active
> connector, like there were 3 different chains

For that to work at all, there would need to be either 2 (or 3) seperate SCSI 
buses.  I have a SCSI PCI card that has 1 internal 50 pin connector, 1 
internal 68 pin connectory and 1 external 68 pin connector.  I can use any 
two at once.  The controler is smart enough to know which connectors any 
anything on them.

> i just thought if the apple drive was
> terminated that placing the quantum drive
> one connector above the apple drive
> would have it on a terminated chain
> but drive setup doesn't see it

It has been a while, but I recall some limitations on mixing 50 and 68 pin 
devices on the same bus.  If you have a 68-pin controler, you need to put all 
the 68 pin devices first then the 50-pin ones.  I suspect the opposite is 
true if your controler is 50-pin.