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| Linux Kernel Architecture |
User space,
that is, everything outside the kernel, both libraries and
application programs, uses these.
Programs in user space contain system calls that ask the
kernel to do something, and the kernel does so, or returns
an error code.
Many things are handled by the C library(System Libraries) itself - those are
the things the user could have programmed himself, but need not
since the author of the library did this job already.
Maybe the presence of the library also saves some memory:
many utilities can share common library code. But for the basic things, starting programs, allocating memory,
file I/O etc., the C library invokes the kernel.
System call interface, which implements the basic functions such as
read and write. Below the
system call interface is the kernel code, which can be more accurately defined as
the architecture-independent kernel code. This code is common to all of the
processor architectures supported by Linux. Below this is the
architecture-dependent code, which forms what is more commonly called a BSP (Board
Support Package). This code serves as the processor and platform-specific code for
the given architecture.