for teaching, documentations and presentations, m$ wondows does the jobs...
Mac cost around $3000 in the states, probably more in uk....
once you get into shell environment, everything is cli based. unless your field requires details of technologies and hands-on experience, you might find mac cost you for nothing...
An Information System (IS) is any combination of information technology and people's activities using that technology to support operations, management, and decision-making