Re: [vox-tech] brain dead hardware question: power pc vs x86 scsi

[Jeff Newmiller <jdnewmil@dcn.MAPSdavis.ca.us>]

On Sun, 9 Sep 2001, ME wrote:

> One thing with laptop SCSI on PCMCIA is power. Desktop based cards seem to
> be better at pushing greater distances of cable with daisy-chained SCSI
> deviced while laptops seem to lack the power, or shielding, or ? to deal
> with the longer busses. (If you have lots of devices on a bus connected to
> a laptop and they dont work, shorten the bus and remove some devices and
> remoboot to see if it starts working.)

The issue is current sourcing capability, which translates to power
rating.

[...]

> 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.

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.

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.

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