[OS X TeX] tlmgr : how to update bin-texlive

[Alain Matthes]

Hi

When I run tlmgr -gui I get this message if I select update

bin-texlive

A comprehensive distribution of TeX and friends.

  A comprehensive TeX system that you can
install on your hard disk. It includes
support for most Unix architectures,
including GNU/Linux and and for Windows. The
MacTeX is developed as part of the the TeX
live effort, and has similar properties, but
is distributed separately. The TeX, PDFeTeX,
XeTeX and LuaTeX engines are provided in the
distribution, with several different running
formats each. Beware: the download is large
(>1Gbyte); it comes in the form of a ISO
image for a DVD, lzma-compressed.

I don't understand : I download what  exactly ?

It is not possible to update only some binaries ?

Best Regards

Alain