Finding the requirements for the software can be hard but a tester has to know when the software breaks and what it takes to run the software. If the tester runs at minimum requirements and it breaks then the requirements are wrong. Some times it is up to the developers what it runs on, some times upper management, and sometimes a tester runs several test. This will also have to be well analyzed and documented. You will also have to take into consideration your market and what kind of computer they have. If it takes to expensive of a computer you loose your market.
Remember to take all this into consideration and many more when setting your software requirements.
QA Hipster is a Quality Assurance Technical Lead for an software company, mostly working with Macs. I have been in the field since September 2013, and have a bachelor's degree in Management Information Services. I started my studies at Iowa State in Software Engineering. I have been working on moving my company forward with the latest QA techniques.