> On Sun, 9 Sep 2001, ME wrote: > > Those 25-pion SCSI connectors are not part of the SCSI standard. Sure > > Apple used them on lots of their boxes and IOMega used them on the SCSI > > and ZIP+ drives, but they are cheating when they do. Whet they do is > > combine several independednt ground lines into only a few so that each > > previously independent ground now is shared. Though SCSI is rather robust > > in many cases and can even "work" with risk/loss in performance without > > ermination, and seem just fine with the 25-pin connectors, they are not > > part of the official pinout standard AFAIK. On Sun, 9 Sep 2001, Jeff Newmiller wrote: > Be careful... I don't think you should suggest that a scsi system can EVER > be set up without exactly two (not zero, one or three) termination points, > located at the ends. Termination is not the same as sharing grounds. > Most SCSI interface cards come with a termination option... in some cases > it amounts to these ten-pin resistor packs that you can insert or removed > as needed. These two were not confused. The point was that todays SCSI adapters are mord robust than earlier controllers. Though you *could* choose to not terminate one end of some busses in use today and still see data move, it is not advised. (Demonstration of robustness being greater by demonstration of being more tolerant of people breaking standards such as poor terminators that may be passive and have insufficient reflection dampening as opposed to active termination. If you had a poor termination at one end of earlier SCSI busses with older controllers, the devices would often just not work. Now, a bad terminator or lack of a terminator on many moden buses can still allow the devices to "work" with risk of data corruption, drops in spead and degredation in performance. The issue with the ground is yet another place where a compnay may not follow the standard and newer controllers do a better job of dealing with 25-pin SCSI than older controllers. (Also plays to robustness.) Also, the issue of required termination was covered in the later portion of my first e-mail that you chopped off of this in your response. (re-included it here:) > On Sun, 9 Sep 2001, ME wrote: > > Make sure both ends of the SCSI bus are "terminated" Don't > > terinate devices in the middle of the bus, only the ends are > > terminated. > Also I won't depend on the "termination" switch on a zip drive... ever > since I lost all the data on all my hard disks due do unreliable > termination by the zip. I use a 25-pin termination block. Yes, on the ZIP SCSI (non plus) I think they used passive termination and have had some that were not "perfect" (bad resistors, or other reasons that may include more shortcuts to save money.) I have had some ZIP SCSI drives that had such poor termination with their switch that they would not even work on the older cards until I placed a good terminator on the end of the bus. Of course, IO Mega's Zip drive still uses that 25 pin SCSI connector which is also a cheaper shortcut that is not in the SCSI standards, so it is possible they may have found other shortcuts with passive termination that is not part of the standards of SCSI. -ME -----BEGIN GEEK CODE BLOCK----- Version: 3.12 GCS/CM$/IT$/LS$/S/O$ !d--(++) !s !a+++(-----) C++$(++++) U++++$(+$) P+$>+++ L+++$(++) E W+++$(+) N+ o K w+$>++>+++ O-@ M+$ V-$>- !PS !PE Y+ !PGP t@-(++) 5+@ X@ R- tv- b++ DI+++ D+ G--@ e+>++>++++ h(++)>+ r*>? z? ------END GEEK CODE BLOCK------ decode: http://www.ebb.org/ungeek/ about: http://www.geekcode.com/geek.html Systems Department Operating Systems Analyst for the SSU Library
