.. _design:

Operating-System Design and Implementation
========================================================

Design Goals
---------------

* At the highest level, system design is dominated by the choice of hardware
  and system type.

* Beyond this level, the requirements can be divided into two groups: user
  goals, and system goals.

    * User goals include convenience, reliability, security, and speed.

    * System goals include ease of design, implementation, maintenance,
      flexibility, and efficiency.

Implementation
------------------------------

* At first, operating systems were written in assembly, but now C/C++ is
  the language commonly used

* Small blocks of assembly code are still needed, especially related to
  some low level I/O functions in device drivers, turning interrupts on and
  off and the :ref:`ts` for :ref:`sync`.

* Using higher level languages allows the code to be written faster. It also
  makes the OS much easier to port to different hardware platforms.