If you're looking at the specifications of your computer
and you notice a section that describes memory,
or somebody asks you how much memory is inside
of your computer, they're referring
to the amount of random access memory, or RAM.
We're not describing the size of an SSD
or the capacity of a hard drive.
We're referring to the components inside
of your computer where all of the transactions
are taking place.
When you're using the programs and the data on your computer,
they're moved off of your SSD or your hard drive
and they're put into RAM so that you can perform calculations
on that information And then store that information back
on the SSD or the hard drive when you're finished.
Your desktop computer or your laptop
will have slots where you can install the random access
memory modules.
The different motherboards may have different types of slots,
but it makes it very easy to add, remove, or upgrade
the memory that's in your system.
The process of moving information in and out
of memory is happening all the time inside of your computer.
So the faster memory you have, the faster
the overall performance will be of your computer.
Every motherboard will be a bit different
on how fast these transfers can occur in and out of memory.
So check the documentation of your computer
to see exactly how fast you can expect your memory to run.
The type of physical package that
installs into those slots on your motherboard is a DIMM.
This is a dual inline memory module.
It's called a dual inline memory module
because this memory module has a series of contacts
on one side of this module.
It has another set of contacts on the other side
of the module.
And those two contacts are different on each side
of that memory module.
These dual inline memory modules have a 64-bit data width,
so we're able to transfer data from these memory modules
in chunks of 64 bits at a time.
The memory that's inside of a laptop
is probably a smaller version of the DIMM.
This is the small outline dual inline memory module,
and it's about half the width of a standard DIM
that you would find in a desktop computer.
You can find the DIMMs and the SO-DIMMs
available in DDR2, DDR3, and DDR4 flavors of SDRAM.
We'll explain what all of those are later on in this video.
If you're using a SO-DIMM, it's probably inside of a laptop
or a mobile device because of the size.
You're able to fit a lot more information
into a smaller area, which is important
for those mobile devices.
Here's a good size comparison of these two.
The DIMM is the larger memory module
that you would find in a desktop computer.
And the SO-DIMM, you can see, is about half the size,
and you would find that in laptops
and other mobile devices.
The type of random access memory that is on these DIMMs
is called a dynamic random access memory.
It's called dynamic because it constantly
needs to be refreshed.
This is very different than the type
of memory you might have in a flash drive,
where you would store information and then
unplug it to move it to another computer.
That flash drive doesn't need to be constantly refreshed
to maintain that information.
But the memory that we use inside of our computers
is a much faster memory and it requires
this constant refreshing to be able to maintain
the data that's on those DIMMs.
If you were to power off your computer, and no longer able
to refresh that memory, everything
that was inside of those DIMMs modules would soon disappear.
The use of the word "random" inside dynamic random access
memory is because we can access anything
in that memory at any place at any time.
This is very different than how we used to access information
on a magnetic tape, where you'd have to wind through the tape
to get to the section that you'd need to read.
With dynamic RAM, you can simply specify an address,
grab that information, and then be able to access that data
The type of dynamic random access memory
that you would find on today's computers
is a type called synchronous dynamic random access memory.
It's synchronous because it is synchronized
with the common system clock of your computer.
The standard flow of communication
based on these clock cycles allows the system
to cue things up at a very standard format.
This is different than earlier types of dynamic random access
memory where there was no synchronization.
But in today's desktops and laptop computers,
all of the memory that we're going to be using
will be synchronous DRAM.
Here's the way that we're able to use these clock
cycles to be able to pull information off of this memory.
In a single data rate memory, or SDR,
we have a single clock cycle.
You can see the up and down wave of the clock cycle.
And there's a number of clock cycles listed on this diagram.
And through each single clock cycle with the single data rate
memory, we can pull one bit of data,
which means if we have one, two, three, four, five,
and six different clock cycles then
we can pull six different pieces of data.
With dual data rate memory, we still
have the same clock cycle.
Things haven't changed as far as the clock going up and down,
and having those six different clock cycles.
The difference with double data rate memory
is that we're able to pull information
on the upside of the clock cycle and the downside of the clock
cycle, meaning that there's two different bits of data
that we can gather in the same clock cycle.
That's where the double in the double data rate comes from.
In older computer systems, you might even
find double data rate generation 2, or DDR2 SDRAM.
These are memory modules that were faster
than the original double data rate memory modules,
and they're not backwards compatible with those.
In fact, they're not forward compatible either.
If you have a computer system that requires DDR2,
then you must use a DDR2 module in that system.
You're not able to replace it with a DDR, a DDR3, or a DDR4.
The generation of memory after DDR2
is DDR3, or double data rate 3.
DDR3 ram has twice the data rates of DDR2,
so greatly improved performance for those systems that
could support DDR3.
It also improved the maximum size on a single dem
to 16 gigabytes of memory.
And, again, if you have a motherboard
that requires DDR3 memory, then you
must use a DDR3 memory module.
You can't take the DDR2 modules from an older system
and move them into a DDR3 system.
They won't fit into the module slots at all.
One of the newer generations of DDR memory is DDR4.
This fourth generation of memory has speed improvements
over the third generation, and it increases the maximum size
of a single DIMM up to 64 gigabytes per memory module.
And, as you might expect, the changes with DDR4
also mean there's no backwards compatibility to earlier
versions of modules either.
Not only did we change the technology
between these different generations of DDR memory,
but we also physically changed the package.
So when we say that it's not backwards compatible,
it's not even an option.
You can see there is a key, or a small slot,
that's inside the memory module, and the slot
is in a different place in each generation of memory type.
This means that if you have a motherboard that
expects DDR4 memory modules, this
is the only type of memory module
that will physically fit into the memory slot.
If you're trying to install a memory module in a computer
and you notice that it's not fitting perfectly,
it may be because you have the wrong type of DDR memory.