.. _abstractions:

File System Abstractions
==========================

The view of files, directories and file systems that is presented to users
and applications is nearly entirely an *abstraction*.  We begin by looking at
the characteristics of drives and hard drives as the primary example.  From
there, we will describe how the abstractions are formed.

.. describe:: Secondary Storage

   Storage that is permanent. Files may be stored on secondary storage devices.

Physical Hard Drives
----------------------

.. figure:: hard_disk.png
   :align: center

Zone Bit Recording
----------------------

.. figure:: zbr.png
   :align: center

Disk Partitions
------------------

.. figure:: partitions.png
   :align: center

Disk Block View
----------------

.. index:: Logical Block Address, LBA

.. figure:: disk_blocks.png
   :align: center

.. describe:: Logical Block Address (LBA)

   Modern hardware uses **LBA** where the secondary storage device
   presents to the operating system numbered blocks of data.  The firmware
   on the device handles the details of where (e.g. track and cylinder numbers)
   the data is stores.

A File
========

.. figure:: file_blocks.png
   :align: center

   A file is an ordered collection of data blocks

Directories and File System Tables
===================================

.. figure:: dir_inodes.png
   :align: center