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is it the end of the line for SCSI Terminators?

by Zsolt Kerekes, editor

See also:- (parallel) SCSI SSDs, What is SCSI?, Storage History
When I first started using SCSI devices as a systems integrator in the mid 1980s the answer to - how many drives you could actually hang onto an inhouse made ribbon cable? - seemed to depend on trial and error.

In those days everything had little mechanical switches, called DIP switches, which enabled you to set up important configuration info such as the SCSI address and whether or not the terminators were to be connected on this device or not. The rule of thumb was that you had to connect the first and last devices physically looped on the chain of cables. Of course that helpful information failed to provide a simple solution to the artistic patterns of daisy chains intermixed with star offshoots around the back of the cabinet which our ingenious wiring people sometimes came up with. It was hard to get them to accept that sometimes a single long loop worked better than a lot of little limpet like add-ons.

When working on a group of so-called "identical" systems I would sometimes be mystified by an intermittent fault in one storage system, even when all the indivdual parts tested as OK. On closer inspection I might discover that some drives had the terminator resistor packs plugged in, while their counterparts in their twin systems didn't. The culprit would often be another project, which in the middle of the night cured their own problems and got closer to customer shipment by "borrowing" components from our own system, which they knew was still a long way in advance of the critical path.

A week or so later, I might be handed a packet with a bunch of terminators and told "These are to return the ones we borrowed." I learned to keep a secret stash of these little suckers for this type of emergency.

Eventually we learned of the existence of SCSI analyzers and other similar test equipment, which was plug and play, instead of the plug and fall off variety when we tried to see what what going on by hooking up about 30 test clips from a logic analyzer. That woudl produce insights only until another project pinched the analyzer, and deleted the custom trace settings... What do engineers do for entertainment nowadays? - I wonder.

Now things are a lot easier with almost everything controlled by software. Smart active terminators can measure the characteristics of the cabling and reflections on the line on reset and dynamically adjust the termination. With serial connections like Serial Attached SCSI and Serial ATA, the problems of data skew, cross talk and reflection are greatly simplified by the simpler cabing design. But proper termination still has a role in reliable system integration, even if its tacky details are invisible to the user.
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parallel SCSI ad from 2003

above - a SCSI cable and accessories ad. This was the last parallel SCSI cable ad which ran on StorageSearch.com and dates from 2003.
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"SSD is going down! - We're going down!"
Surviving SSD sudden power loss
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Adaptive flash care management & DSP IP in SSDs
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Always make sure that your SCSI is properly
terminated... Megabyte suddenly remembered.
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With SCSI, the computer uses a standard set of commands to move data back and forth between host and peripheral. For the peripheral vendors, this means writing one driver for each operating system environment, as opposed to one driver for each computer vendor.
What is SCSI?
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SCSI terminators manufacturers

(this list is no longer updated)
Advanced Electronic Support Products

Cables East

Ci Design

Computer Cable Makers

CS Electronics

Dun Cheng Technology

Granite Digital

Hurricane Computer Products

IMP

Information Systems Supply

Interconnect Solutions

Methode Electronics

Micro Accessories

PDE Technology

RAM Electronic Industries

Relax Technology

Selectronix

Shine Wire Products

Technical Cable Concepts

Texas Instruments

TMC-The Mate Company

Ultra Spec Cables

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