What means the fat .gch file?

[J.C. Pizarro]

2007/11/1, Jack Lloyd <lloyd@randombit.net> wrote:
>
> The .gch files are precompiled headers for C++ which speeds up
> processing of the often large templates used in the STL.
>
> Please send questions about gcc to gcc-help@gcc.gnu.org, this
> list is only for discussion of the development of GCC.
>
> Regards,
>   Jack
>
> On Thu, Nov 01, 2007 at 10:19:59PM +0100, J.C. Pizarro wrote:
> > $ du -s /opt/gcc4*/include/c++/4.*/i686-pc-linux-gnu/bits/
> > 33793   /opt/gcc41320071029/include/c++/4.1.3/i686-pc-linux-gnu/bits/
> > 64743   /opt/gcc42320071031/include/c++/4.2.3/i686-pc-linux-gnu/bits/
> > 181     /opt/gcc43020071026/include/c++/4.3.0/i686-pc-linux-gnu/bits/
> >
> > In /opt/gcc4*/include/c++/4.*/i686-pc-linux-gnu/bits/ there are
> > * 33.65 MB of stdc++.h.gch/ from gcc-4.1-20071029
> > * 32.38 MB of stdc++.h.gch/ from gcc-4.2-20071031
> > * 32.20 MB of stdtr1c++.h.gch/ from gcc-4.2-20071031
> > *        0 MB of no such dir. stdc++.h.gch/ from gcc-4.3-20071026
> >
> > O0g.gch and O2g.gch from these dirs eat many MBs of disk space. Why?
> >
> > What is there inside of fat .gch file? What means the .gch file?
> >
> >    J.C. Pizarro

Thanks,

But why gcc-4.3 has not precompiled header for C++
and gcc-4.2 has two redundant precompiled headers for C++?

Why not these precompiled headers for C++ in /var/cache/ instead of local dirs?