How much disk space does Android OS 4.1.1 take?
There's a difference between "how much the Android OS requires" and "how much the manufacturer reserved". Remember, the OS has its own partition (/system), which is mounted read-only during normal operation (just made writable for OS updates), while the user's data goes to /data. Moreover, most manufacturers add their own "presents" (also known as bloatware) to the /system partition.

So while the actual Android system usually fits into less than 1 GB (considered there are devices shipping with less internal storage), your device's manufacturer might have decided to reserve more space for future updates and his own add-ons.