IT may be complex, but from the perspective of the business, it is just a lot of technical gubbins that sits between the screen and the data. Users access applications and systems with no real clue about what goes on behind the scenes, nor any desire to understand more than how to change a toner cartridge. We can rail at their …
Performance and scalability
Are the same thing in this context, aren't they?
Performance is an absolute, in that it shouldn't drop below a certain threshold, even as the number of users, or the amount of traffic scales. I've seen a few application architectures that were not built for the latter, which meant silly rules had to be imposed for example around the number of concurrent users. In which case, performance was maintained but the system couldn't really be said to be scalable!