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"Drop in Compatible" are the 3 Words That Scare me the Most

by Michael Bowling, on Jan 3, 2018 10:14:52 AM

What designers of long-life computing systems need to know

We’ve all been taught to never trust somebody that says, “trust me.” As a computer engineer by training, the words, “Trust me, it’s drop in compatible” scare me like few others. If I were a client designing a long-life, mission critical, certification-bound computing platform that I’ve spent months, or longer, defining my specification, qualifying in my lab that everything works perfectly for my application (hardware, software, firmware, BIOS, etc.), gone through months of certifications (CE, UL, vibration, shock, etc.) and NOW you tell me to trust that you believe a new part will work perfectly, it would concern me greatly.

Many computer suppliers promise product longevity so that the exact computer configuration will be available for many years to come…but what guarantees do I have that the supplier didn’t make changes that they feel are “drop in compatible?”  I understand that sometimes changes are necessary…but they should be a last resort and I want to make sure that an actual engineer approves the changes—not a buyer or comptroller trying to save pennies.  So just what can I do to make sure my supplier has the proper revision control processes and procedures in place?

Communicate up front what your expectations are

Let your computer supplier know just how sensitive your application is to revision changes. If you need to verify every single change down to the component level then they need a formal system in place to keep you in the loop. Most applications only want/need to be informed if the change could potentially affect the form, fit, or function of the computer. For example, changing the CPU would have obvious implications on your software and that’s an extreme change…but if a resistor on the processor board changes from 5% tolerance to 1% you may not necessarily want to be involved. There is a lot of grey area in the middle so be open and upfront with your computer supplier about your needs.

Make sure everyone understands what proper revision control means

Most people typically define revision control with the following criteria:

  • Form = physical size and visual parameters of a specific component are the same.
  • Fit = the part physically interfaces with the rest of the system correctly
  • Function = the intended action of the part is correct

If your supplier does not agree with your definition of when you should be notified then you will eventually have an issue down the road when parts begin to change without you knowing.

Proper quality processes throughout the whole company

  • This does not simply apply to the major components and it doesn’t just apply to procurement and production. This applies from the very beginning through End of Life (EOL).  Design, lab testing, procurement & inventory, assembly, QC, etc.  Everyone at the supplier should have proper revision control built into their culture.
  • Make sure that your supplier has thorough assembly documentation and assembly processes. Check their ISO 9001 certificate which will make sure they have been scrutinized by an independent quality professional at least once a year.

Ensure the supplier has a clear process in place to notify you of any form, fit, or function changes and their potential impact.

  • At some point, there will be a definitive EOL of a part with no form, fit, or function alternate that will force the computer, as a whole, to go EOL. Ensure that your supplier has the proper notification process in place to let you know in advance that the product is going EOL. This should be a formal and automatic quality procedure to notify active customers with as much notice as possible. Many times, this notification process is called a Product Information Notice (PIN).

At the end of the day, you are the customer and your computer hardware supplier must have proper revision control systems in place to ensure that your project continues to run as smoothly as originally intended for the whole life of your program.  If any of these concerns apply to your project, contact one of our Engineers to determine how partnering with Trenton can help alleviate your worry about and extend your long-life computing deployment’s lifecycle. 


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