Is there a way to evaluate the minimum requirements of a software? I mean, how can I discover, for example, the minimum amount of RAM that my application will need?
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Ideally, you'd decide on the minimum requirements of a piece of software based on your target audience, and then test your software during development on that configuration to ensure it delivers a satisfactory experience.
You can look at a system running your software and see how much memory is being consumed by your application, and use that to guide how much memory is being consumed. CPU is a little bit more complex - you could try to model your CPU requirements, but doing this accurately can be challenging.
But ultimately, you need to test your app on the base system you are targeting.