Ele contém código específico da arquitetura .
All the architecture specific code is in this directory and in the include/asm- directories. Each architecture has its own directory underneath this directory. For example, the code for a PowerPC based computer would be found under arch/ppc. You will find low-level memory management, interrupt handling, early initialization, assembly routines, and much more in these directories.
Se você procure , você pode ver os diferentes diretórios para arquiteturas como x86, ARM etc ....