[Info-vax] SCSI cable rules.

[Stephen Hoffman]

On 2016-09-01 13:56:37 +0000, Tom Adams said:

> We have DS10s and I am trying to avoid SCSI cable pitfalls.

Please read the old DEC SCSI developer docs for details on how DEC 
envisioned the SCSI pieces would fit together.  Link here: 
http://labs.hoffmanlabs.com/node/54

See other available resources, as well: 
http://computer.howstuffworks.com/scsi4.htm   
http://www.pcguide.com/ref/hdd/if/scsi/prot_Diff.htm  
http://www.pcguide.com/ref/hdd/if/scsi/protLVD-c.html

Stay far, far, far, far, far away from HVD SCSI, until and unless 
you're very sure you have compatible equipment:  
http://www.pcguide.com/ref/hdd/if/scsi/z_t10_iconhvd.gif

Or use some of the old DEC- or Compaq-branded external SCSI shelves 
http://labs.hoffmanlabs.com/node/54 and avoid most of the mess of 
internal drives and cabling and canted connectors and skinned knuckles.

> I have some SCSI cables with no terminator on the end, it was probably 
> a mistake to buy those.  Looks like most of the disks and tape drives 
> we have don't have a "terminator" jumper.  Some have "term power" 
> jumpers. The passive female terminators for internal 68 pin cables seem 
> to be kind of pricy and bulky.
> 
> Can I assume that all the SCSI control cards that work for a DS10 will 
> provide term power so that I don't have to add a device that has term 
> power?

There's little or no reason to put a SCSI terminator in a cable.   Even 
the internal ribbon cables have separate terminators plugged into the 
connector, not integrated into the cable.  Or the terminator is plugged 
into the last device in the chain.   A SCSI terminator is a SCSI 
terminator, differing by details such as wide or narrow bus, active or 
passive, and the specific connector used.

Simpler is better.   Use shelves.   Makes cabling simpler.   Makes 
disks easier to swap.


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