Understanding Basics of File-system

Lets try to understand what is a FileSystem and whats the need for one .

Examples of a FileSystem are ext2, ext3, ext4, XFS,  NTFS, Fat32, Fat16

Lets begin by examining  Human reading and writing skills .

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Honesty is the best policy.
You should Always be honest.

Lets examine .

•  How did you figure out the words (Honesty, best, Always )
•  How did you figure out how many lines are there
•  How did u figure out the alphabets .  H, O, N, E, S, T.

Human brain has been taught the semantics of reading and writing .   The semantics goes by

•  Group of alphabet together with space as delimiter is a word .
•  A new Line is how we discover the start of a line .
•  To read a word one needs to read from left to Right(HONESTY) and not vice Versa(YTSENOH)
•   To read a line we read from left to right and not vice versa.
•   Each alphabet has been associated with a specific sound and a specific way of writing it.   How you pronounce “a” differs from “h” and same for writing it.

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Lets try to understand from CPU perspective how does the world look like .

• Everything is represented as 0 and 1 .
• 0 and 1 themselves are state representation. can be represented as   Voltage +10v => 1 ,   +5v=>0
• CPU  sees no difference at all between different kind of files.
• CPU has no idea of how to read a word , line , sentence paragraph
• All it knows is Binary form of OPCODE PARAM PARAM

Lets try to understand from Hard-disk (Storage ) perspective  how does the world look like

• There are two state it is aware of Magnetized and demagnetized
• The state can be translated to 0 and 1   by some external translator like Drive of the hard-disk.
•  Hard disk is aware of track and sectors.
•  It has no clue of what is a file a directory.
•  It has no clue what is a text file , a c file , a binary file , a java file , a php file .
•  It  just magnetizes , demagnetize tracks and sectors based on the request made by the driver.

Lets try to understand from Operating System (OS ) perspective  how does the world look like

• Operating system interacts with CPU, Hard-disk , Humans and all other resources.
• Operating System takes care of saving a file and retrieving back the info of the file in the same format.
• Operating System understand which application to open for which specific type of file.
• Operating system needs to provide humans view of file and directories
• Operating system needs to interact with CPU in terms of 0 and 1 .
• Operating system  Provides ASCII translation

The catch is Operating System can be shutdown and still it needs to retrieve all info saved in the hard-disk And OS needs to provide the same view of File and directories as it was before shutdown .

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Here comes the part where OS maintains the semantics just like Humans to differentiate file and directories, The semantics in detail cover everything

• How to distinguish file from a directory
• How to differentiate where a file starts and where it ends on hard-disk.
• Just realize its not a human but some code with some logic which can understand the boundaries .
• From hard-disk perspective OS is just getting back a stream of 0 an1 (demagnetized , magnetized)
• Along with actual file some meta info is also being saved this constitutes the data of the File system

File system is the logical semantics to maintain data on a storage system . It also has a physical representation in terms of meta info (Example ext4 layout) .

FileSystem logic is also extended to maintain a in memory fileSystem known as /proc fileSystem in linux.

Linux Provides a variety of commands to explore and work on file system