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from Ekeeda Hello friends in this video
now we will discuss information
management in detail in the previous
video we have already studied about the
three areas in which operating system
divided services so they are information
management process management and memory
management in this video we will have a
look on information management in detail
concept related to information
management now as I said information
management is basically dealt with for
file so whenever we create a file
whenever we read a file whenever we
write into a file whenever we create a
directory all the system calls they
comes under the category of what
information management so we have to
keep it in our mind that information
management is something which is related
to whole file so let us have a look on
information management number one is a
file system now what is a file
as I said file is a collection of what
information and that information can be
numeric it can be alphabetic or it can
be alphanumeric so file system allows
user to define a files or create a
directories and allocate and D locate a
space to H file files are mapped by
operating system on physical devices so
as I said a file is a collection of what
information and it can contain a program
and data and it can be a numeric
alphabetic or alphanumeric and each file
has a extension for an example if you
are creating the HTML file we have
already studied studied HTML so in that
case we have studied key to create HTML
file we give a extension as dot HTML if
you are creating a document file then we
give extension as dot do see if you are
creating a text file then the extension
will be dot txt so what they have to say
is each file has a name and each file
has what its extension now there are two
types of file system number one is
called as FS system and number 2 is
called as this base system now a base
system has been tripped
list by dismiss system now no one uses
step based system in early days we used
to use what a basis ting now what was
the best system in the pavement system
there was a physical real so the problem
with the physical real was it was very
long and your data works small so more
number of files we used to store on that
physical ring so finding a particular
file from the physical real was a time
consuming so this problem was replaced
by the disk based system so what they
have to say about the best system will
have a look on it early file systems
where they've missed and as I said the
best means what it was having physical
wheels so physical tape reels are large
but most of the files are small so more
number of files we used to store on a
one tape a directory is added to a tape
which lists the name and location of
file on the tape but the problem was
finding the file was very time-consuming
so this was replaced by disk based
system in the dismissed system we have
it tracks and a sectors so your base
disk is basically divided into track and
tracks are further divided into a sector
each sector contains a unit of
information so let us see what they have
to say the problem with the tempest are
resolved in the disk this in a disk
based system a disk is use and disk are
divided into tracks your tracks are
further divided into sectors and this a
sector is what a smallest unit of
information a sector vary from 32 bytes
to 4:09 6 bytes so this is basically a
disk based system next we will see what
is blocking it is a unit of data which
operating system defines for the sake of
convenience from hardware point of view
this consists of sector but from the
point of view of OS this consists of
what blocks and each block has one or
more sector so what we have studied this
contains what tracks and tracks contains
what sector so from the hardware point
of view at this consists of sector but
from the point of view of operating
system here this consists of what block
and
each block has one or more sectors into
it so file is considered to be a
sequence of block and all basic
input/output functions operates in terms
of block next we will see what are the
file operations now see there are
several file operations like creating
the file writing a file reading a file
providing the file and deleting the file
now we will discuss each operation in
detail
number one is creating a file now to
create a file first we see whether
specified space is available for that
file is check so obviously when we
create a file as we discussed in the
beginning of this in the beginning of
this topic only when we create a file
first we need to see give me the
specified amount of space is available
or not to create a file if the space is
available then only operating system
allows us to create a file so for
creating a file first specified space is
available or not that is check and if it
is available then entry for the new file
is made number 2 writing a file for
writing a file there is a command in
which name of the file is given then
operating system searches for that file
in a directory and then writes to it
suppose if I want to write into a ABC
file then first I will search whether
ABC file is available on the disk or not
if the ABC file is available on the disk
then only I can write into the file so
first operating system has Pro search
whether ABC file is available or not
next is reading the file I can to read a
file we need to do the same thing
suppose if I want to read a ABC 5 then
again I have to see whether ABC file is
present in the disk or not the operating
system will search for the ABC file if
the ABC file is present in the disk then
we can read the file number four is
rewinding the file again for rewinding
the file the directory is searched for
appropriate entry so again I have to see
another ABC file is there of the disc or
not if it is there then my file is reset
to the beginning of the fact so what is
basically rewinding the file when we
start from the beginning I called it as
what rewinding next is deleting the file
again suppose if I want to delete ABC
file then again until
I need to search whether ABC file is
present in the disk or not if it is
present in the disk then I can do a
delete operation so students and this
thing you have understood that searching
operation we are doing repeatedly so for
this what operating system does
operating system makes a list of files
which are recently used now suppose as
in the previous example I was constantly
doing the operations on what ABC file so
instead of searching ABC file on full
directory operating system will create
one list in that list you will make it
will make sure that all my constantly
used files are open this case operating
system don't have to search for thee
such in the entire directory instead of
searching for the entire directory
operating system will search that ABC
file into the list of open files so it
will take a less time to search that
particular file next is access method
now there are two types of access method
number one is called a sequential access
at number two is called as direct access
now see what they have to say about the
access method file stores information
and when it is used this information
must be accessed and read into a
computer memory so as I said there are
two ways in which we can access the file
you can access your file directly or you
can access your file sequentially now
sequential method is very simple if you
are using your C if you are using a
sequential method then in that method
you have to access the file in
sequential way as we have studied file
consists of what file is a sequence of
blocks so now suppose if my file is
divided into eight blocks so I have a
block from starting from number one to
number ten and if I am using the
sequential access method then in that
case suppose if I want to access a block
number five then I have to start
accessing the file from block number one
then I will access block number two then
block number three then October four and
then block number five so this type of
method is called a sequential access
method now the problem with the
sequential access method is to access
block number ten you have to start with
the block number one so we can go for
the
another method and that method is called
as direct access in the direct access
method you don't have to go sequentially
now suppose a family looking for a block
number two then I don't have to start
from block number one I can directly
jump on to block number two suppose if I
am looking onto a block number 15 then I
don't have to go from block number one
to block number 14 I don't have to do
that I can directly jump from block
number two to block number 15 so this
type of method is called as direct
access method now see a file is a view
as a sequence of blocks this we have
already discussed a file is a consists
of what sequence of block and in this
method any block can be read or written
so we don't have to go in this equation
we can read a block 14 then 53 then we
can write block 9
anyway there are no restriction of order
of reading and writing yes there is a
restriction in what sequential access
method in the sequential access method
you have to go sequentially but in the
file access method you can jump onto a
any block as you wish next is allocation
method the direct access to a nature of
disk allows us to store many files on a
same disk so there are three major
methods of allocating our dismiss number
one is called as contagious number two
is called as link and number three is
called as in mix so we will see each
location method in a detail so let us
start with the contagious before
contagious there is one topic called as
free space management it is necessary to
reuse a space from deleted files for a
new file C as I said your memory is what
limited so you have to use your memory
in very efficient way so in that case
you should not waste your memory you
have to reuse the memory so to keep a
track of free disk space the file system
maintains of free space list to create a
file it's search free space list for
required amount of space and allocated
to a new file so when we create a file
first it will search for what free space
list means first it will see whether the
specified amount of space is available
or not to create a file if it is
available then it will allocate a member
I mean it will allocate that space to a
file
this space is then removed from the free
space list obviously
initially suppose if I was having a 50 M
B's with me
and suppose I have created a file of 10
MB then that T Nimbus will get deleted
from the free space list and now your
free space list is updated now how many
how much memory you're left with you're
left with now 40 and B's memory so this
is called as what free space management
this space is then removed from the free
space the free space list is implemented
as a bitmap so each block is represented
by one bit so if the block is free your
bit is 0 if your block is not free if
your block is allocated then your bit is
what 1 so this is called as what free
space management you know let us come
back to the topic contagious our
location
what is contagious or location in the
contagious a location B a look at a
space in a contagious way it means
address will get allocated in a
contagious way so contagious a location
method requires each vari to occupy a
set of contagious address contagious
address means suppose if my first block
is told 1001 then obviously my next vlog
will get store on thousand and two then
my next block will get stored on
thousand and three so this type is
called as what contagious our location
so suppose if you are allocating the
first block in thousand and one and if
you are allocating the second block in
thousand and five then this is not
allowed you have to allocate a space in
a contagious way like in re in re what
we do address towards this arrest OC
data in what contagious way so same
thing is applied over here
continuous allocation of file is defined
by disc address of the first block and
its length so how did you find the
address by the disk address by the disk
address of first block and its length so
if the block is in block long then sky
it starts at location B so but if your
block is in block long and if it starts
at location B then it will occupy B then
my next will be V plus 1 the Manics will
be B plus 2 dot dot dot it will be B
plus n minus 1 so in this way here that
DJ's allocation method works
next thing is dynamic storage
the next thing is dynamic storage
allocation a dead space is a collection
of free and use segments each segment is
a contagious the set of this block and
other located segment is called as a
whole a dynamic storage allocation
problem is how to satisfy a request of
size from a list of free whole so there
are three techniques first fit best fit
and was feed our use now what is dynamic
storage allocation what they are saying
at this space is a collection of what
free end your segment obviously in the
disk space we have some segments which
are free we have some segments which are
what are located now those are the free
segments I called it as what holes okay
so we have three techniques basically in
this first fit best fit and boss fit we
will see each technique in detail what
is per speed in the first fit it
allocates the hole first hole that is
big enough so searching can be start
either at the beginning of the hole or
where the previous phosphate ended and
we can stop the searching as soon as we
find a large enough hole next is called
as best fit in the best fit it are
locates the smallest hole which is big
enough so we must search the entire list
unless the list is kept order by size
next is worst fit in the worst fit it
allocates what it allocates the largest
hole now we will see all these three
techniques with the help of example now
let us see our first fit based fit and
was fit techniques with the help of
example now suppose if I have these are
the available blocks which I have in the
first weight what will happen suppose if
I get a request of size of three ma now
in the first field it will allocate a
first hole which is big enough now see
my request is of 3 MB so if I'll start
from the beginning of the list then I
will get here what 10 MB so 10 MB is a
first hole which is big enough to
satisfied what 3 M B's so 3m B's will
get allocated in this enemies so the
earth there will be wastage of what 7m
B's in the best fit best fit it will
allocate a smallest hole which is big
enough now if you'll go through the list
then which is the smallest hole which is
big enough to set
ready request yes 5mb so this three
ambhi's we'll get allocated isn't this
five Emmy so again there will be a
wastage of what two Emmys in the worst
fear it will allocate the largest well
which is big enough now which is the
largest whole 30mb is the largest rule
so it will occupy three ambe's input
30mb so here there will be a wastage of
what 727 MB so if you will see in
everywhere there is a vestige of memory
but as compared to a best and first fit
in the worst fit there is a large amount
of what memory wastage now this vestige
of memory is called as what
fragmentation now there are two types of
fragmentation number one is called as
internal fragmentation and number two is
called as external fragmentation we will
see what is fragmentation in detail in
the in the concept of what memory
management so I hope you have understood
what is the first best end was fit
technique with an example in the first
fit what we do we are located first one
which is big enough in the best fit we
are locate a small hole which is big
enough and in the worst fit we are
located largest world which is big
enough to satisfy the request so these
are the three techniques which we use
and you can say worst fit technique is a
vast technique because it wastes a more
memory as compared to one first and best
fit
now the next technique is called as link
or location now see this is the list of
this block which are which I have so -
block starts from this number 1 2 3 4 5
6 7 8 and so on and it X I 24 now in the
link the location I will be having a
starting address with a lisp block and
ending address of a lisp low so suppose
if the starting address is 9 then I have
to start from block number 9 then from
lot of the time I will search for a next
entry now suppose if the next entry is
at block number 7
then I will directly linked to a block
number 7
now suppose get the next block is at the
top number 12 then I will link to the
block number 12
now suppose it in next block is number
15
then I will link or block number 15 and
if the last law is a 21 then I can link
here
21 so this is this is called as what
link a location where your file is a
linked list of this block so if you say
if you see here my file is a linked list
of this block starting from block number
nine to block number 21 this is somewhat
related to one linked list in the linked
list also be used to do that only we
used to have a file entry of the first
block and then we were having the
address of next block and be used to
link before block with the address of
next block so in the same thing here
also be our link in the address of first
block with the address of next block and
so on so this is called as what link
aggregation now let us see link a
location in a detail so in link a
location each file is a linked list of
disk block and this disk block may be
scattered anywhere on the disk so as I
as we saw example we were having around
our 24 blocks and those 24 blocks were
scattered on the disk a directory entry
content pointer to the first and last
block of the disk so we saw neither
having the first block and that flaws
block was pointing to block number 9 and
my last block was finding to block
number 21 so what I did I started from
lock number 9 and then I ended at where
block number 21 so when we create a file
each directory entry has pointer to the
first block of the file and this pointer
is initialized to nil so when we create
a file basically what happens each
directory entry points to what first
block of the file and that block is
initially all what it is initially mean
so of right to file removes the free
block from the free space list and
writes to it so right to file what it
will do I will remove the block number 9
and then I will start writing into a
block number 9 this new block is then
linked to the end of the file for an
example suppose I started from 0 of
number 9 then my next block was block
number 7
so my block number 7 will get attached
to block number 9 I mean it will get
attached to end of the block number 9
then after block number 7 I was having
what block number 12 so block number 12
will get attached to block number 7 so
in this way my link allocation will
happen or it is my money
collocation will work so starting from
block number nine next block I was
having was block number seven then next
block I was having was block number 12
and so on this new block is then linked
to end of the file and to read a file be
simply rates block by following pointers
from block to block so in this way we
have to suppose if I want to read a
block number 12 then I have to start
from lock number 9 then I will I will go
to the block number seven and then I
will go to the block number 12 so here I
get two advantage any block can be used
to satisfy a request as you have seen we
we are not doing anything in contagious
way like I started with the block number
nine and then I jump back onto a block
number seven then I jump back again onto
a block number twelve so I used any
block to satisfy request and there is no
need to declare this size of file when
it is created now what is the
disadvantage here we get to read block
number twelve I started with block
number nine then I jump onto block
number seven and then I jump onto block
number two it so major problem is that a
link allocation can be used effectively
for what sequential method so this was
about the link allocation now the next
method we have that is index allocation
in index allocation all pointers are
brought together into a one location
called index block so here you will have
one block in o in that block all your
pointers will be you know all your
pointers will get stored into that block
and that block is called as what index
block so it means here pointers are not
scattered now your pointers are there in
the one block and that block is called
as what index block so each file has its
own index flow so the eyes entry points
to the right block of the file to read
eyes block we use the pointer in the
eyes block entry and when we create file
is created all pointers in the index
book are set to name so basically when
file is created all pointers in the
index block are set to a name now we
will see what is index block with the
help of example then you will understand
it more clearly now see this is
example of indexer location now suppose
if this is my these are my this block
and this is problem number 16 I called
it as in text block now in this in place
loss I have the pointers to all and
those pointers are 9 7 12 and 21 so same
example I have taken up the chart which
are taken for in Glinka location now in
killing the location what I did I
started from block number 9 then I jump
onto talked them to 7 then I don't want
to block number 12 and then I ended up
block number 21 but in this case if you
see see I have Index blocks that is 2016
so I called it as watch index low and in
this index blocks are happy pointers to
all other block so then basically I will
point to for block number 9 I will jump
from this index floor to polyglot number
9 then when next block comes clock
number 7 again from the index flop I
will jump to block of the 7
now next block number 12 so from index
block I will point to block now bit with
and the last is not block number 21 so
if you compare this method with the in
technique a location you can see key in
this block I can I in this method I can
access a new block so I don't have to go
in sequential way suppose if I want wax
is lock number 7 then I did it you jump
onto a block number 7 right so because
the n52 blocks are not interconnected to
each other all my entries are done from
their index flow so this is called as
what index a location I hope you have
understood this topic of information
management now in the next video we will
talk about process management
thanks for watching
you
