<p>Why does C++ Builder 6 always compile all files? </p>

<p>I make some changes on one file but BCB 6 compiles all files when I start the app. Any idea? I use Windows XP SP2.</p>

Are you source files and binary objects located on the same machine? If not sounds like you have a network time sync issue.
If they are its most likely a header file issue, either the compiler include files have a modified date some time in the future or your application is dependent on some header file that changes during compilation say from a COM import.
EDIT: Check the setting VS has a flag to always re-compile, this might be true for BCB too, if set then unset it. Another possibility is that pre-compiled headers are miss-configured to generate on every source file.
I am not familiar with BCB 6 to give a more precise answer.