Welcome to our new lecture
In this lecture we are going to talk about one of the most
important topic which is
MEMORIES Now in computer how many types of memories are
there and what are their functions that we are going to
know in this lecture
So watch this lecture very carefully because in exams if
any questions come then it is bound to come or generally in
competitive exams if any questions are asked then they come
from this topic means they come from this topic or from
this topic only
So one of the most important topic
So let's see what all things we are going to see
So let's go to white board and on white board first of all
we see here it is written computer memory
I will increase its size a little so that things become
visible
So first of all what is written here that a computer is
like a human brain means computer's memory that is just
like a human brain what all things we can do in our human
brain
whatever information is there
I am reading a book next day I have exam so all those
things which are there in that book will be stored in my
mind
I don't know how to make Maggi My mother gave me
instruction that first you have to do this second you have
to do this so those instructions are stored in my mind
I don't know how to make tea My mother said do one thing,
first pour water then add sugar and tea leaves means first
I added water so this is step one in second step I added
tea leaves and sugar then I waited for it to boil so what
are these things these
are my instructions means step by step how to make
something now when these things are told to me what
happened to me when I went to school for the first time
there you remember the way in one or two times how do you
remember because things are stored
in your mind so our mind is nothing it works like a memory
means whatever things you want to store in it you can store
it same thing with computer computer also has a memory if
you want to store any kind of data you can store it there
so here it is said
a memory is just like a human brain like a human brain the
same thing what happens in computer memory and we had
studied when we had seen the starting lectures what is
called memory
CPU is called brain like a human brain it is used to store
data and instructions what did I just say
I just said we store instructions in human brain we store
instructions in human brain that I have to make something
there are some steps of making my mother told me and next
time when I go to make
I will remember that thing
I remember the data how I remember the data
I went to buy something from the market and from the market
I got to know that the price of this product is 100 rupees
now when I gave 100 rupees
I remembered that I have bought the thing for 100 rupees
means that thing became data when my mother will come home
and ask me what will I say 100 rupees how can I tell things
because it is stored in my human brain that data is stored
in my computer that
information that instruction is stored in my human brain in
the same way we store the memories in the computer how we
store them in the memory now memory is of different types
like secondary storage in secondary storage you store your
pdf file images
you store videos songs in the same way there is a memory
which we call storage device there also things are stored
in the memory like human brain computer memory is the
storage space in computer means what is computer memory it
is a storage space where
data is to be processed and instructions required for
processing are stored let's try to understand he is saying
that computer memory is storage space means this is my
storage ok in this storage storage means where you can
store things and this area is
space storage space in computer where data is to be
processed and instructions required for processing are
stored now see whatever data is to be processed like I said
2 plus 3 so this operation of sum will be processing here
my 2 and 3 give me a second
here 2 and 3 this is my data so this data will be stored
here apart from this operation will be processing 2 plus 3
this instruction will be stored in storage space of
computer this is written here the memory is divided into
large number of small parts
called cells means this is my memory this is my memory is
divided like this like this whole memory and it has a size
particular size let me make it then you will understand
what we are talking about ok this is my cells all these
like this this is my cell
1 this is my cell 1 cell 1 this is my cell 2 cell 2 like
this all these boxes are my cells so my memory that memory
is divided into large number of small parts like this this
is called cells here it is written large number of small
parts called cells
each location of cell has a unique address means it will
have an address it will have an address it will have an
address now understand it like this if I tell you this
picture I have drawn do you see anything different you will
say no all are same now
if you have seen apartments being built like in colleges
houses are built like this like this like this like this
now when you see from outside or when you go to society all
the houses you see are same but how can you differentiate
it you know that address
of this house will be different address of this house is
101 here Sharma ji lives here his address is 102 here other
Sharma ji lives his address is 103 so you can store things
inside this house that I have a bed inside my house
I have a TV inside my house
I have a person inside my house
I have a kitchen inside my house
I have a refrigerator inside my house like this you can get
things in 102 like this you can get things in 103 like this
you can get things in 103 so all these cells we can see
they all have an address and this address is of everyone
and how much space
they will take inside it will depend on the type of data we
will try to understand it later we will try to understand
it later for now what you have to understand that my memory
is divided into cells and what happens to these cells there
is an address
and what is this address it is a unique address every
cell's address will be different no two cell's address can
be same which varies from 0 to memory size minus 1 which
means if your memory size now when you go to buy a memory
card what they used to
say give me a memory of 8 GB give me a memory of 4 GB
suppose what is the total size of this memory its total
size is 8 GB so what you will say you will say how much
these will vary from 0 to 8 GB 8 GB means 2 power 8 and
from here minus 1 like this for
example if computer has 64 K word 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024
64x1024 64x1024 64x1024 64x1024 64x1024 64x1024 you can see
cache memory here, it can be in different places in
different motherboards but there are some types of
motherboards where it is installed, so you have to
understand that you go and see cache
memory, let me show you, we went to google, what we did
here, we put cache memory, see how it looks, let's go to
images and in our images, this will be our cpu, this will
be our cache memory, this will be our main memory, this
will be our secondary memory,
so who is the closest to the cpu, cache memory, after that
main memory and this is our secondary storage, so here what
is cache memory, cache memory you can see here, is there
any image on the motherboard, is there any image, it is
shown in this way,
this is like a chip here, means chip is of one type, which
you will see, like this cache memory is installed, so what
will you see on the motherboard, you will see something
like this, like this thing is installed, so what will you
call it, you will call
it cache memory, let's go ahead, now let's talk about our
primary memory, how did we understand primary memory,
we saw that there is one thing, what happens, our primary
memory is like a playground, let's make it here, what
happened to us, it became a playground, means if you want
to run any app, then it will have to come to this
playground, what will have to bring,
our executable file, executable file means whatever code is
written in 101, it will have to come here, this is it,
primary memory holds only those data and instructions on
which computer is currently working, means it keeps only
that data, on which work
is currently going on, how, let's
understand, you opened an application, like what did you
open, you have to run the photoshop application here, so
where will photoshop have to come, it will have to come
inside the RAM, so the executable file of photoshop is
photoshop.exe, the executable
file came here, you saw the
interface of photoshop, now in photoshop, you will take
some photo, what will happen to that photo, that is data,
so where will you see that data, it will be shown inside
this app, the instruction will be shown inside this app, so
what happens, it will
only store this
data, it will only store this data, it has limited
capacity, and data is lost when power
is switched off, try to understand the difference between
secondary memory and primary memory,
secondary memory is your, in which you have put some
things, like I have downloaded a video, now from secondary
devices, till I go and delete it, it will not be deleted,
now like I am teaching you, while running it, what I have
opened, I have opened microsoft
whiteboard, I have opened chrome, all these things are open
where, means whiteboard.exe
file is running in your ram, your chrome.exe file is
running in your ram, suddenly light goes off, so both these
files will be removed from there, will be removed from ram,
means the nature of ram is temporary, your power goes,
power goes, switch off,
so whatever data you have, it will be lost, okay, capacity
is also less, and data is also lost, it is also lost, so
this is the difference between primary and secondary
memory, primary memory is generally made up of a
semiconductor device, these memories
are not as fast as registers, registers are faster than
this, this thing is also to be understood, the data and
instructions required to process reside in main memory, so
whatever data or instructions required to process reside in
main memory.
we have very large scale integrated circuit, after that we
have ultra large scale circuit, so here it is called
semiconductor memory, because when their memory is
manufactured, then what is used inside them, semiconductors
are used, it is known as main
memory, what is it called?
It is called main memory, usually volatile memory, volatile
memory is there in which
faster than secondary memory,
it is also known as external memory or non-volatile memory,
it is slower than main memory, these are used for storing
data information permanently, CPU directly does not access
these memories
inside, they are accessed via input output routines, it
means that my storage means that my hard disk drive will be
saved, my CPU can't do it directly, it can't communicate
directly that I want this file, I want this, how will it do
it?
It will do it through input output routines, contents of
secondary memories are first transfer to main memory, that
is, whatever content is inside the secondary memory, it can
be a song, it can be an application, it can be a software,
where is it transferred
first?
It is transferred first inside the main memory and then CPU
can access it, and when can CPU access it?
When it is transferred, for example, disk, CD-ROM or DVD,
these are some examples of secondary memory, what are the
characteristics of secondary memory?
These are magnetic and optical memories, now what we have
read, what are the primary memories?
These are magnetic and optical memories, what is the
meaning of magnetic, we just saw that inside the image, is
the image visible here, let's see once, yes, this image is
visible, but it is not visible from inside, so I will show
you, see, here we put
magnetic memory, magnetic memory, this will come to us,
okay, see this, it happens in this way, it works like this,
see this, see this, what is this, all are magnets, what is
this, these are magnetic cores, this is your magnetic
memory, let's go back,
what is here, it is known as backup memory, that is,
nothing is deleted, now see, like here some of your content
is increased, your content is increased in secondary
storage, where will that content come to you, it will come
to the primary memory, it
comes to the primary memory, after that, your computer is
switched off, or electricity is gone, what will happen in
that case, in that case, brother, this will happen, that if
this data was also lost with me, then how would I work, so
this is kept as
a backup, that is, you have opened a song in any software,
in any application, like you have opened Spotify and you
are listening to songs in Spotify, what happens suddenly,
suddenly my life is lost, so what will happen in that case,
in that case, it will happen that the app that was open in
your primary memory, it will be closed and that song will
also be removed from there, so if that song is used as a
backup.
If my data is not stored in secondary storage, then you can
think that my song also gets deleted.
It is not like that. It is non-volatile memory.
Data is permanently stored even if power is switched off.
It is used for storage of data in a computer.
If you want to store data on a large scale, like if you
want to store a 4-5 GB video or a movie, then you can
easily do it in this.
Computers may run without secondary memory.
It means that even if there is no secondary memory in the
computer, it will work.
But the computer...
See, it is written in English.
It may work or it may not work.
So, it is not like that it will work.
It may not work.
After that, is it slower than primary memory?
We know that secondary memory has always been slower.
So, we understood the difference between primary memory and
secondary memory.
Now, let's see what it looks like.
The hard disk drive that I have looks like this.
Now, let's talk about random access memory.
Random access memory is the internal memory of the CPU.
It means that it is the internal memory.
And what is my storage?
It is my external memory.
So, remember this difference.
For storing data, programs and program results.
What does it do?
It stores program data and program results.
It is read and write memory.
You can read and write data in it.
It stores data until the machine is working.
As long as the machine is working, the data will remain.
If the machine is not working, the data is over.
If the light is off, the data is over.
As soon as the machine is switched off, the data is erased.
That is, the data is removed from there.
Access time in RAM is independent of the address.
That is, each storage location inside the memory is easy to
reach as other locations.
And takes the same amount of time.
That is, if you want to store and access data in RAM, you
can easily do it.
You can easily reach its location.
And it will take the same amount of time.
Data in RAM can be accessed randomly.
But it is very expensive.
That is, you can access it randomly.
But it is expensive.
That is, your RAM is very expensive.
RAM is volatile.
That is, data stored in it is lost when we switch off the
computer.
What does volatile mean?
Once the computer is switched off, the data is lost.
If there is a power failure, the data is lost.
Hence, a backup uninterruptible power system, UPS, is often
used for computers.
You must have seen that UPS is used.
What is UPS?
Uninterruptible power system.
That is, suppose your power is lost.
If the power is lost, then UPS gives you a backup of power.
For 15 minutes, 20 minutes, or half an hour.
So that you know that I am working in a software and
suddenly the power is lost.
All my data will be lost.
It is better that I get a warning that the power is lost.
I will quickly store the data and save it.
I will work on it when the power is restored.
RAM is small.
Both in terms of its physical size.
If you compare it with storage, it is small.
And in the amount of data it can hold.
And it holds less data.
RAM is of two types.
You get to see two types of RAM.
You get to see static RAM.
SRAM is called dynamic RAM.
Now let's try to understand.
What is the meaning of static RAM and dynamic RAM?
I have already seen the picture of this RAM.
How does it look?
Now let's see what the meaning of static RAM is.
The word static indicates that the memory retains its
contents as long as power is being supplied.
That is, as long as you supply power, your content remains.
However, data is lost when the power gets down due to
volatile nature.
If the power is switched off, your data is lost.
If the power is lost, the data is lost.
SRAM chips use a matrix of six transistors.
Now this is understandable.
SRAM chips use a matrix of six transistors.
And no capacitors.
That is, you do not get to see capacitors in it.
If someone asks you whether SRAM has transistors or
capacitors, you will say that there are no capacitors.
Here are transistors.
And what are transistors?
They are a matrix of six transistors.
Transistors do not require power to prevent linkage.
That is, they do not need power.
So SRAM need not have to be refreshed on a regular basis.
That is, you do not need to refresh it.
What does refreshing mean?
Suppose you have seen this thing.
Whenever you go to fill a form, there are some images to
know whether you are a human or not.
You have to select where the car is in these nine images.
If you understand that you can refresh it, what will happen
if you refresh it?
A new image will be generated.
Or sometimes you fill a captcha.
What happens in a captcha fill?
You do not understand a number.
When you do not understand a number, what will happen in
that case?
In that case, it will be simple that I can refresh it.
What will happen as soon as I refresh it?
As soon as I refresh it, I will see a separate captcha to
fill.
So here, there is no need to refresh in SRAM.
But it is in dynamic RAM.
Because of the extra space in the matrix.
SRAM uses more chips than DRAM.
That is, static RAM uses more chips than dynamic RAM.
For the same amount of storage space.
Thus making the manufacturing cost higher.
The more components you put, the higher the cost.
So SRAM is used as cache memory and has very fast access.
So this static RAM is also called cache memory.
What are the characteristics?
It has a long life.
There is no need to refresh.
There is no need to refresh again and again.
It is faster.
Used as cache memory.
It has a large size.
It is expensive.
It has high power consumption.
That is, it will consume as much power as possible.
After this, let's see what is written in our dynamic RAM.
Let's try to understand what is written in it.
Dynamic RAM.
Read only.
Memory.
One second.
Read only memory.
We will not do storage in this lecture.
We will do storage in the next lecture.
Because if we include storage in this lecture, it will be a
big lecture.
So let's try to understand what is dynamic RAM.
Let's understand it.
What does dynamic RAM mean here?
DRAM unlike SRAM.
Must be continually refreshed.
That is, it needs to be refreshed again and again in order
to maintain the data.
If you want to keep the data, you will have to refresh it
again and again.
What will happen if you don't do it?
It will not work.
This is done by placing the memory on a refresh circuit.
That is why this memory is kept on a refresh circuit.
That rewrites the data several hundred times per second.
That is, it rewrites it hundreds of times per second.
DRAM is used for most system memory.
That is, the use of DRAM.
You know where DRAM is used.
DRAM is used in most system memory.
Because it is cheap and small.
SRAM is expensive.
DRAM is cheap.
All DRAMs are made up of memory cells.
Memory cells are composed of one capacitor and one
transistor.
In this, one capacitor and one transistor are installed.
In SRAM, there are transistors and no capacitors.
In dynamic RAM, one capacitor and one transistor are
installed.
What are the characteristics?
It has a short data lifeline.
That is, the data lifeline is very short.
Need to be refreshed continuously.
That is, you need to refresh it again and again.
Slower as compared to SRAM.
Compared to SRAM, it is slow.
It is clearly visible.
Use as RAM.
Lesser in size.
Use as RAM.
Less expensive.
Less power consumption.
Power is also consumed less.
Read-only memory.
You can't write things in this.
You can read things on this.
How can you read?
Let's try to understand.
ROM stands for read-only memory.
Something like this.
This is how I see it.
You will get to see this in Badarpur.
ROM stands for read-only memory.
The memory from which we can only read
You can only read but can not write on it
What can be the example of this? We will talk about
examples only
This type of memory is non-volatile
I had understood the difference between non-volatile and
volatile
What is volatile? What is non-volatile?
What is volatile? Tell me
Non-volatile means that
Your content will be there
That content will not be deleted
You can not write on it or re-write
This information is stored permanently
In such memories during manufacture
That is, the manufacturer
What do they do?
They store this information
Tell me how?
There is a read-only memory in the computer
When I turn off the power of my mobile
Tell me
It is written in it
Can you change it?
You can not
If you turn off the Windows computer system
It is written on it
A mobile used to come
Nokia 1100
Tell me
Can you change it?
You can not
It is written on it
Manufacturer writes on it
ROM stores such instructions
That are required to start a computer
Those instructions
Which start your computer
This operation is referred to as bootstrap
When your computer is turned off
It is called bootstrap
In bootstrap, there are some instructions
These things will be checked
What can be done in instructions?
Check if there is RAM
Where will the executable file go?
Your computer will not be turned on
This operation is called bootstrap
Where are these instructions stored?
They are stored in your ROM
Who manufactures it?
Manufacturer puts it
ROM chips are not only used in computers
It is not that it is only used in computers
It is used in mobile phones
But also in other electronic items
It is also used in washing machines
How is it used in washing machines?
How is it used in microwave oven?
They have made buttons in the microwave oven
Can you change it?
If I press this button, the food will be hot
If I press this button, the temperature will be high
The display comes
If I click on it, the temperature will be shown
I cannot change all those things
Manufacturer has given it
That's it
There are many types of ROM
Let's read mROM PROM EEPROM EEPROM MROM- Masked ROM
Masked ROM
The very first ROMs were hardwired devices
Hardwired Device contains a pre-programmed set of data
So, if you have pre-programmed data, set of data,
instructions, then what I will say?
I will say that this is my mROM, what is pROM, what is
pROM, it is a program that is used to store data in the
mROM, it is a program that is used to store data in the
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