Custom vs. COTS

What’s the best way to achieve all of the requirements of your new system? Should you go down the bespoke route and develop custom built hardware and software that fits the bill perfectly, or should you go for Commercial Off The Shelf (COTS) hardware and software and maybe compromise on some of the non-functional requirements? Zircon has been involved in both camps and has formed the following views.

Our experience of bespoke systems has come from the rail industry where safety approval means that systems have very long lifetimes. Type approval of road systems provides the same scenario and every industry has its reasons for not updating. The systems become reliable as they start to climb the later end of the bathtub curve, and obsolescence means that spares become as rare as rocking horse droppings.

Software that is completely bespoke, right down to operating system or scheduler or whatever, rapidly becomes a black art. The engineers that understand the software leave (retire) and replacements that can, and are willing to, work on old software, are very hard to find. Fixing and adding functionality to this software is extremely difficult.

COTS is not a clear cut answer! The “Betamax syndrome”, backing the best but not taken up technology, is common. How many Multibus 11, STEBus and VME Bus systems are still in operation, clinging onto life only due to the dedication of a technician? In safety critical systems, can the level of testing required be achieved if the system includes a COTS operating system?

A custom built solution means that you are in complete charge of every facet. You can tailor the hardware and software to the minimum required functionality, and nothing more. This level of control comes at a high price if you are building low volume, high availability, long life systems.

Provided you avoid the Betamax, the problem of obsolescence is eased and spares are readily available.  COTS hardware also gives you the advantage of having someone else do the R&D necessary to exploit technology advances.  The amount of work required to enhance the functionality of a system is greatly reduced.

Picking the right operating system, one that provides the required functionality and safety, means that your software can also keep up with technical advances. Open standards may mean that you can import software functionality that has already been tried and tested. Also, of course, the task of finding engineers to develop, maintain and enhance software running under a COTS operating system is greatly reduced.

So to conclude, if you are developing a high volume, low functionality, short life system then bespoke is for you. If you have to develop a system that you know will outlive you and will need to be enhanced, COTS is the smart choice.