SCSI drive jumpers?

[dudejediknight]

I guess this is the right place to put this... forgive me if it isn't, but nothing else seemed to fit.

I've been looking around for some SCSI drives for some of my old Macs that need them, and I came across a listing for "SCSI jumpers". The listing says they're "Used for SCSI, SCA, Laptop, and FC drives (Not used for IDE drives)". They're described as being 2.00mm in size. Further research on my part tells me that the ones used on CD/DVD drives and IDE/ATA hard drives are 2.54mm.

Not having dealt with SCSI drives before, this was news to me. Through my travels, I gathered an assortment of drive jumpers from various dead drives that were being discarded. (Can you really ever have too many spare jumpers?) Some were taken from some old PC floppy drives, and were visibly smaller than the standard ones I'd seen. Since they were free, I figured that they may come in handy if I ever needed a smaller jumper for something.

Since I got the old Macs without any SCSI hard drives in them, I can't do a direct comparison. I'd hate to buy a SCSI drive to find out it didn't come with jumpers, and that the ones I have won't work. Do SCSI hard drives really use different jumpers? Does that also apply to all internal SCSI devices (like SCSI CD/floppy drives)? Could those smaller floppy jumpers I've accumulated be the same ones used on SCSI drives, or are they something completely different?

 

[equill]

As you have already deduced there are different sizes. ATA/IDE drives do use jumpers for selection of Master, Slave and Cable Select when it is necessary, and they use the wider 2.54-mm units.

SCSI drives generally use the 2-mm jumpers unless there is an attached adapter for SCA (80-pin) to 68-pin or 50-pin, or 68-pin to 50-pin kludging. (It works, but it is a compromise that needs care in the doing.) Elsewhere, as for enabling termination, motor start, start delay, parity enable/disable, write protect, termination power supply and anything that I have forgotten, 2-mm jumpers of various heights (to fit the available spaces around the drives) are used.

Parity, write protect, motor start and spin-up delay are either not often, or never, of concern with HDDs in Macs. As a generality, older Quantums need no jumpers. Their termination resistors are physically removed if necessary, and only SCSI ID=0 is acknowledged. Later, but still old, HDDs allowed for SCSI ID selection (in case of additional drives in the daisy-chain) with three jumper pairs, and a pair for enabling termination (by means of on-board ICs) if necessary.

Modern drives vary greatly in jumpering needs depending on the make of HDD. Again as a generality, Macs are likely to need TE (if physically last on the cable), TP (which can come from the drive or the bus) to power the termination circuits and MS drive start, and disabling of funny-bugger features (eg IBM drives) such as unit attention and sync. negotiation. Jumper patterns for their HDDs are published by most manufacturers, even for old drives. If you can't find what you need, post what you have on your drives and someone will advise you.

de