OS is the abbreviation of operating system，The OS we used
most like Windows MacOS and Linux. Each of them is different
another one and one representation of a OS.
An integral OS contains six parts. (hardware management,proc-
essing management, mermory management, networking managem-
ent,security management, file system management). For most people,
Windows may be the most friendly OS，but not all. For example a
GEEK more likely to choose Linux for work.
Why Linux? Through this link maybe you will find the answer.