MAC Operating System Question:

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OS X is a BSD Unix based operating system with a GUI which is more user friendly than Windows for many users. The OS allows for permissions based accounts, and has better access controls to limit the spread of malicious software (yes, there are viruses and proof of concepts which target Apple software), and protects the system folder from write actions unless a user has administrative privileges.
The ease of use is often cited as a primary reason for educational institutions and art related business to defer to Apples.
Windows is prevalent in business environments, and has differing architectures based upon which flavor is installed (there are vast differences between 3.11, 95, 2000, XP, Vista, and 7) and the variations would best be researched on a product information site. Because of the popularity of Windows, malware and viruses are numerous, and an antivirus program is often the bare minimum that a user must use to protect their computing resources and data.
No matter the operating system, a best practice to follow is to always work from a user account with limited privileges and only do upgrades and installs from within the administrative account's workspace.