The Windows equivalent of
HOME is the user-specific
application data directory. The actual location depends on the
Windows version; typical values are C:\Documents and
Settings\username\Application Data on Windows 2000/XP/2K3,
C:\Users\username\AppData\Roaming on Windows
Vista/7/2008, and either C:\WINDOWS\Application Data or
C:\WINDOWS\Profiles\username\Application Data on Windows
9X/ME. If this directory does not exist or cannot be accessed, Emacs
falls back to C:\ as the default value of
You can override this default value of
HOME by explicitly
setting the environment variable HOME to point to any directory
on your system. HOME can be set either from the command shell
prompt or from ‘Properties’ dialog of ‘My Computer’.
HOME can also be set in the system registry,
see MS-Windows Registry.
For compatibility with older versions of Emacs1, if there is a file named .emacs in C:\, the root
directory of drive C:, and HOME is set neither in the
environment nor in the Registry, Emacs will treat C:\ as the
HOME location, and will not look in the application
data directory, even if it exists. Note that only .emacs is
looked for in C:\; the older name _emacs (see below) is
not. This use of C:\.emacs to define
Whatever the final place is, Emacs sets the internal value of the HOME environment variable to point to it, and it will use that location for other files and directories it normally looks for or creates in your home directory.
You can always find out what Emacs thinks is your home directory's location by typing C-x d ~/ <RET>. This should present the list of files in the home directory, and show its full name on the first line. Likewise, to visit your init file, type C-x C-f ~/.emacs <RET> (assuming the file's name is .emacs).
The home directory is where your init file is stored. It can have any name mentioned in Init File.
Because MS-DOS does not allow file names with leading dots, and older Windows systems made it hard to create files with such names, the Windows port of Emacs supports an init file name _emacs, if such a file exists in the home directory and .emacs does not. This name is considered obsolete.
 Older versions of Emacs didn't check the application data directory.