Operating System Structure

In Windows operating systems, the root directory is <drive_letter>:\ (commonly C drive). The root directory (also known as the boot partition) is where the operating system is installed.

Directory	Function
Perflogs	Can hold Windows performance logs but is empty by default.
Program Files	On
32-bit systems, all 16-bit and 32-bit programs are installed here. On
64-bit systems, only 64-bit programs are installed here.
Program Files (x86)	32-bit and 16-bit programs are installed here on 64-bit editions of Windows.
ProgramData	This
is a hidden folder that contains data that is essential for certain
installed programs to run. This data is accessible by the program no
matter what user is running it.
Users	This folder contains user profiles for each user that logs onto the system and contains the two folders Public and Default.
Default	This
is the default user profile template for all created users. Whenever a
new user is added to the system, their profile is based on the Default
profile.
Public	This
folder is intended for computer users to share files and is accessible
to all users by default. This folder is shared over the network by
default but requires a valid network account to access.
AppData	Per
user application data and settings are stored in a hidden user
subfolder (i.e., cliff.moore\AppData). Each of these folders contains
three subfolders. The Roaming folder contains machine-independent data
that should follow the user's profile, such as custom dictionaries. The
Local folder is specific to the computer itself and is never
synchronized across the network. LocalLow is similar to the Local
folder, but it has a lower data integrity level. Therefore it can be
used, for example, by a web browser set to protected or safe mode.
Windows	The majority of the files required for the Windows operating system are contained here.
System, System32, SysWOW64	Contains
all DLLs required for the core features of Windows and the Windows API.
The operating system searches these folders any time a program asks to
load a DLL without specifying an absolute path.
WinSxS	The Windows Component Store contains a copy of all Windows components, updates, and service packs.