ImageMagick 6.8+ and Rmagick is not installing on windows 7

C:\Sites>gem install rmagick
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing rmagick:
        ERROR: Failed to build gem native extension.

        C:/RailsInstaller/Ruby1.9.3/bin/ruby.exe extconf.rb
checking for Ruby version >= 1.8.5... yes
checking for stdint.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=C:/RailsInstaller/Ruby1.9.3/bin/ruby
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler
 failed to generate an executable file. (RuntimeError)
You have to install development tools first.
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:506:in `try_cpp'

        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:931:in `block in
 have_header'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:790:in `block in
 checking_for'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:284:in `block (2
 levels) in postpone'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:254:in `open'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:284:in `block in
 postpone'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:254:in `open'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:280:in `postpone
'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:789:in `checking
_for'
        from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/mkmf.rb:930:in `have_hea
der'
        from extconf.rb:193:in `<main>'


Gem files will remain installed in C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9
.1/gems/rmagick-2.13.1 for inspection.
Results logged to C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rmagick-2
.13.1/ext/RMagick/gem_make.out

gem 'rmagick', '2.13.1'