Most (commercial) linux distributions install their x86_64 version as a mixed environment. This means that the 64 bit libraries are installed in /lib64 and /usr/lib64, while the usual directories /lib and /usr/lib contain 32 bit libraries which are necessary to run 32 bit applications. Debian, on the other hand, provides a pure x86_64 distribution (the amd64 port), where the 64 bit libraries are installed in /lib and /usr/lib. 32 bit libraries are either installed below /emul (through the ia32-libs package) or in a completely separate chroot environment. The chroot environment has the advantage that it uses the normal i386 packages and can even be updated with “apt-get dist-upgrade” separately from the 64 bit installation. 32 bit applications like OpenOffice run very well in the chroot environment, and even building i386 packages is possible. The only disadvantage is that the chroot environment can take up a significant amount of space. The real problems arise if you need to install a 64 bit application which uses an installer which is built as 32 bit application. No one does this? Sure. Oracle does. And they require a mixed installation. There seems currently no way to install the Oracle client on an amd64 debian installation.