I've heard this statement a few times.
"There are no functional changes to the system, just a bunch of non functional updates to hardware and software."
What I really hear is:
"We are changing broad areas of the system, but we're not adding any buttons/fields/pages/widgets so we're going to classify this as a non functional project."
This sort of assumption needs to be challenged. If you are changing the foundation of a system, there cannot not be any functional changes! The reaction and interaction of a systems users dictates function. For clarity a user can be a human or another system in this context.
Do the following count as 'change?'
- System changes speed: If the system responds slower or faster, those using it will respond to that. Improving your performance can have negative impacts on the consumers of your system, if the user expects a certain speed of response.
- Systems inherent fragility changes: If the system has more or less availability this will change interaction. Expectations will rise (or fall), so might volume!
Remember, if you convert your teapot to be made from chocolate, its function is the same but it's behaviour is pretty different!