On Thursday, April 22, 2004, at 12:38 PM, Byron Q. Desnoyers Winmill wrote:
On Thu, Apr 22, 2004 at 11:44:11AM +0800, John Niven wrote:Yes, I understand but doesn't that mean that the motherboard already
has a terminator built in? So if I used an internal (terminated) drive,
and an external (terminated) chain, I would have:
Term <-> drive <-> Term (MB) <-> drive <-> Term
If you pull out the power supply, you will notice a second internal SCSI connector. I believe that is for the "external" SCSI bus.
Yes I have seen that connector which gave me the idea of using two internal drives, one off each MB SCSI controller. But what worries me is if the second one supplies a terminated internal drive, how does that effect the use of the external SCSI connector? Like this:
Term <-> internal drive <-> mainboard 2 <-> external SCSI device <-> Term
If Mainboard 2 also has termination haven't I got too many terminators?
So I still need to know if the Apple CDROM acts as a terminator, or if I have to add a terminator to the cable.
My guess would be no. I took mine apart, and didn't find any evidence of the supporting electronics (I found pads which would probably hold the electronics, but they were quite unoccupied). It does make sense: in most cases Apple would have sold these as external units, in which case external terminators or the norm; or they would have sold them as part of a system, in which case the hard drive would have provided termination.
What happens in Macs that have a SCSI CDROM and an IDE HardDrive? I don't know the parentage of my Apple (12X) CDROM, so I guess maybe I should open it up and have a look :-O
I am currently running it (in the Q950) without a terminator, and with Term power off. I works fine except, when I have my JackHammer NuBus SCSI card plugged in I cannot boot from a CDROM. When I remove the JackHammer it will boot. I'm very confused!
That's one of the reasons I was considering ditching the JackHammer and using the dual MB interfaces instead.
John
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