Everybody and welcome to the next video on the Linux operating system module.
And this video when we talk about the Linux files and more specifically the 64 file system.
So what is the sixty four sixty four or extended file system version four is those commonly used file
system for Linux today.
It's what's gonna be in the Ubuntu install that we should have installed in the previous video.
And it's also was built to improve on security features speed performance etc. on the previous E X T
three and there was multiple such as the two and then regular X team.
These are all previously done versions.
Now what does he look like.
He has a few sections here so we've got the boot sector which contains the boot code the grub loader
which we'll talk about in other videos.
Just know that that handles the booting process.
We have block group 0 which is a very special block group which will go over in a second and then block
group n which is just standing for in any amount past that point so block one block or two and then
unused sectors is just empty space at the end that can be used for more block groups.
It tends to keep the empty space there just in case but we don't need to worry about that.
In this video now four relies on a series of blocks to hold all of its data together and these blocks
are in turn grouped up into block groups which makes it easier for the file system to find out where
a file is located.
If it knows a block group number or it knows a block it's block number which then it can know which
block group to look in so it doesn't have to scan the whole file system and look for one file.
Now it's important to understand that everything in in Linux is a file so the keyboard monitor drivers
everything is a file the network connectivity is all a file in Linux just allows things for quicker
lookups.
Now data blocks data blocks are sectors on the disk.
There are between 1 kilobytes and 64 kilobytes depending and this is where the data is stored.
Obviously in the physical medium so the file and directory can have multiple data blocks that define
them based on how big the file.
So if a file is 1 meg it's going to have quite a bit of data blocks associated with it then something
with one Kilbey.
So the first block group which is block group 0 has a little bit of a special padding at the very beginning.
That's 1024 bytes.
It's used by the OS installation or any any issue any oddities or backwards compatibility issues that
go into this.
This first thousand twenty four bytes and then past that point we're having the standard block group.
So this is again this is the standard block structure we've got the super block group descriptors data
block that maps the I note bit maps the I know tale and then the actual physical data blocks.
Now what does a super block super block is think of this is like the master record for the block.
Now this contains the information around the file system that that it's in control of the number of
blocks in the group.
The number of nodes which will go over in a second supported features maintenance information but there
there's hundreds of options here so there's a link above the video that will go into much more detail
around super blocks and the whole four file system as a whole.
Now group descriptors we're gonna brush over this pretty pretty quickly.
They're not always used it just holds a table of the bitmap locations as well as the I know table.
Now this is stored in a few other places as well.
So the grid script is not always needed unless these sparse super feature flag is set.
Otherwise it won't.
However there's parts of it that still stick around because it required this table also holds data around
the Directory accounts in the blocks how many directories are there where they're located.
Now the data and I node block bit maps.
Now it holds and tracks the usage of the data blocks within the block group.
So this also includes entries on where the eye nodes are now.
Just a quick high overview and I note is think of an eye node as a file so it references a single file
such as the date time stamp.
What block it's associated with etc..
A bitmap.
Just in case you a few of you are not aware a bitmap tends to use one bit at a time to represent some
sort of status for something whether it's on or off enabled disabled.
Whatever the case might be in this case it's for the data block and where the note entry is so last
bit.
Here is the new table which holds again the I note holds the metadata for the file so date time block
map location etc..
This table handles all files or the eye nodes for every block in its block group.
So if this I know table vanishes you lost your data.
So this has just been a quick high overview of the x 4 file system.
Again the more much more details are available in the link above.
This is just kind of to get you familiar with the concept of what I nodes are and how the file system
kind of works.
So when we go into other details where we actually go into AI nodes the word blocks is not foreign to
you at any time.