From what I understand.
The bottom Layer (the "base" or the "root") is the guts of the operating system. Here are the system files a user never sees, and should never mess with. Here is where input/output is controlled, and how memory and disc access are managed. Nothing here pertains to the normal user. So all these files are locked down and require the highest access level to be able to modify.
An administrator will need access here to perform a system update, or add a new feature (second hard drive, new graphics card, whatever). Otherwise it is left alone , So this layer requires root access
The middle layer is the file system and the applications/programs. Depending on the way the computer is used and the ability of the user, this layer and the upper layer may use the same access level or they may be split. Assuming the machine is fully compartmented, then a supervisor might have middle level access so he can add and remove programs and change permissions of shared file systems. But he is not a "guru" so he does not have "root" access.
The top layer is the user layer. In a locked down machine, the user can open and run programs they are set up for them, store data where the supervisor has designated, and read files they have permissions for. Otherwise, they are locked out of the machine, and cannot change or view areas outside their boundaries.
Why does windows not use the 3 layers like Linux ,Unix and Mac OS x?
And is all Linux have 3 layer system like Unix and Mac OS X
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