Thanks for your all reply, especially cr88192.

That is, in linux different processes share the the same code(Dlls),
but in window they copy the code to their space.

Now we have a global variable(g_var) in Dlls, in linux if one process
change the *g_var*, and does it effect another process?

by the way, what's the different between 'load time' and 'running
time'. Does 'OS' control 'load time'?