This directory level abstracts out the Linux Operating System dependent features of uClibc for supported Linux architectures/CPUs. If you wanted to port uClibc to some new Linux architecture (arm, mips, etc), this is the place to add that support. All stuff that is not at all dependent on a particular Linux architecture goes in the 'common' directory. However, for new architectures which are using the generic syscalls in the Linux Kernel, the 'common-generic' directory should be used instead as they all use identical interfaces for the system calls.