Trying to use Ediff with Windows 7

Hi.

I am running Windows 7 on an HP computer.

I downloaded:

http://mirror.lagoon.nc/pub/gnu/emacs/windows/emacs-25.3-i686.zip

It unzipped fine and I have a folder `bin' (among other folders) with
file `runemacs.exe'.

Double-clicking `runemacs.exe' successfully launches the GUI for
Emacs.  I can choose `Tool' and `Compare(Ediff)' and it seems to work
fine for comparing directories, but, if I try and compare files, I get
the error:

`No such file or directory, diff'

Is this a bug or is it to be expected (given that I am running Windows
7 and the only gnu-related thing I have on my computer is the unzip of
`emacs-25.3-i686.zip')?

I hope someone can clarify this as I am quite confused.

Sincerely,

David Wardle
Auckland
NEW ZEALAND.