Teacher: In this lesson,
we're going to talk all about memory modules.
Now, the type of memory that you are going to use
is going to be determined by the motherboard
and its form factor.
The best practice here is to check your motherboard's manual
for the proper type, size and speed of memory
that you're going to be buying
before you purchase those new modules.
While some motherboards allow you
to mix the size of the memory modules,
others may require you to have all modules
being the exact same size.
Now, when we're talking about the size here,
I'm talking about the capacity,
such as four gigabyte modules or eight gigabyte modules
or 16 gigabyte modules.
For example some motherboards may support
putting an eight gigabyte module in slot one
and a four gigabyte module in slot two,
to give you a total of 12 gigabytes of RAM.
While others would not allow this
because there's a size mismatch there.
And instead you'd have to put in two fours
to give you eight or two eights to give you 16.
And there would be no way to get to 12 gigabytes
on this system
because there aren't six gigabyte memory modules
available in the marketplace.
In most modern motherboards,
you can use what's known as single banks
where you can put any size module into any of the slots
and mix and match them.
But older motherboards did require you
to do things in pairs, and that would be a bank of two
or a paired bank.
Now, when you look at the form factor of your motherboard,
this is going to determine how much memory
you can support on a given system.
This is because you may have only one memory slot
or two or four or eight,
depending on the form factor of your particular motherboard.
If you have a larger motherboard,
it is likely to have more memory slots
and therefore you can have a total higher amount of memory
supported by your system.
Whereas if you're using a smaller form factor motherboard,
you may only have one slot or two slots
and that's going to limit the amount of total system memory
that you can install.
Now, memory modules are going to vary by the type,
which is going to be defined by the motherboard
and its form factor, as we just mentioned.
These are going to define the number of pins
that they have on those modules as well
depending on what series of memory you are buying.
For example, if you're using DIMM
or dual in-line memory modules,
these might have a 240-pin connector
or a 184-pin connector or something else like that,
depending on which one you're buying.
Another classification of the memory chips in the modules
is its type.
Now in past systems, they used different types of memory
based on the manufacturer,
but in most current systems,
we all use the same type of memory
and it doesn't matter which manufacturer you're using.
Instead, we're doing it based on a version
such as DDR3, DDR4 or DDR5.
Now DDR stands for Dual Data Rate.
Now the Dual Data Rate is the most common type of memory
that's going to be used in most systems,
but there are a couple of examples
in some specialty legacy systems
where you might find something like
Rambus Dynamic Random Access Memory,
or RDRAM being used instead.
Now another classification we have
when we look at memory modules is based on their speed.
With older memory,
this was actually classified in nanoseconds.
For example, 60 nanoseconds.
But over time, as we moved into DDR3, DDR4 and DDR5,
those nanoseconds were so fast
that almost all memory looked like it was the same speed
because they were all operating
in that one to five nanosecond range.
So we started calculating this instead based on bus speed.
For example, if you have a PC133 memory,
this operates at a bus speed of 133 megahertz.
Now most modern memory is going to be measured
in throughput though.
Over time though, the bus speed was no longer
a valid calculation either
because almost all systems were operating
at the same bus speed,
and instead, we started measuring memory in throughput.
Now throughput is calculated based on the bus speed
and the width of the data bus.
So for example, if I was using an older DDR2,
which is known as PC2-6400,
this tells me that this is offering
an 800 megahertz bus speed and has a throughput
of 6.4 gigabytes per second of bandwidth.
We can see the 6.4 gigabytes per second of bandwidth
because we see that 6400 number after the PC2,
and PC2 tells me this was a DDR2 module that I was using.
All right, now that we've covered
some of the basics of memory modules,
let's take a look at memory modules
and how they've progressed through time
to our current systems of DDR3, DDR4 and DDR5.
First, we had DRAM, which stands for Dynamic RAM.
DRAM is one of the oldest types of memory
and it required frequent refreshing
of the contents inside of it to make sure it wasn't lost.
DRAM would store each bit of data
or program code in a storage cell
that consists of a capacitor and a transistor,
and is typically organized in a rectangular configuration
of different storage cells.
A DRAM storage cell is dynamic
and it means that it needs to be refreshed
or given new electrical charge every few milliseconds
to compensate for the charge leaks from the capacitor.
Otherwise the data stored in that DRAM will get lost.
As an improvement to this,
we moved into what's known as SRAM or Static RAM.
Now SRAM solved this issue of the constant refreshing,
but it was really expensive to manufacture.
Because of this, SRAM was only used in very high speed needs
such as L1, L2, and L3 CPU caches,
hard disk buffers and LCD screen buffers.
You'll still see Static RAM used today in those caches.
And again, because it's so expensive,
we have a very small amount of that
inside of each of our processors.
Next we have SDRAM.
Now SDRAM stands for Synchronous DRAM.
This was the first memory module
that operated at the same speed as the motherboard's bus.
The initial chips were 168-pin dual in-line memory modules,
known as DIMMs, and they had their speed rated in megahertz.
The common naming conventions for these
were things like PC66,
which means it was using a 66 megahertz bus,
or PC133, which meant it was using a 133 megahertz bus,
or PC266, which means it's using a 266 megahertz bus.
Now, while SDRAM performed at the same speed
as the motherboard's bus,
the CPU itself operates much, much faster
than the motherboard's bus.
To help bridge that gap,
there's a new type of memory module created
called DDR SDRAM.
And this stands for Double Data Rate
Synchronous Dynamic Random-Access Memory.
Now this type of memory can transfer data
two times per clock cycle
and thereby it basically doubles the speed of transfer
over a traditional SDRAM module.
These modules came with 184 pins
to be able to connect to the bus
and they were rated in megabytes per second
as their throughput.
And a good example of this is something like PC-1600,
which provides you with 1,600 megabytes per second
or 1.6 gigabits per second of throughput.
The next type we had was known as DDR2 SDRAM
and this is Double Data Rate SDRAM version two.
This has a higher latency,
but faster access to the external bus,
which gave you overall better speeds.
These chips had a 240-pin connector
to connect their modules into the slot
and they were rated in megabits per second
just like the original DDR was, but at higher speeds.
When you see these written out,
it would be written as PC2- and a number, like PC2-4200,
which stands for 4,200 megabytes per second of throughput
or 4.2 gigabytes per second of throughput.
After that, we introduce DDR3.
and DDR3 stands for Double Data Rate 3 SDRAM.
Now DDR3 runs at a lower voltage
and at a higher speed than DDR2
because it is a newer generation with these improvements.
But again, the latency here actually increased
over those previous DDR2 modules.
But again, because it has a faster speed overall,
the latency isn't that big of a deal for us.
Now, these modules also have a 240-pin connector,
just like DDR2 does,
but each of these modules is keyed.
And what I mean by that
is there's actually a little notch
in the bottom of the set of pins
on the bottom of these memory modules.
Now with DDR2 and DDR3, that notch is in a different place.
So you can't take a DDR2 module
and put it in a DDR3 slot,
and you can't take a DDR3 module
and put it in a DDR2 slot.
They're not cross compatible that way
because of this keying.
Now the common way that we write this is PC3- and a number.
So if you see PC3-10600,
this means that we have
10,600 megabytes per second of throughput
or 10.6 gigabytes per second of throughput
using this DDR3 module.
When it comes to DDR3,
you're normally going to see data transfer rates
or throughput of 6.4 to 17 gigabytes per second,
and a maximum module size
of eight gigabytes per memory module when using DDR3.
Now as an advancement to this, we come up to DDR4 and DDR5.
DDR4 is Double Data Rate version four,
and DDR5 is Double Data Rate version five.
DDR4 is going to have speeds of 12.8
to 25.6 gigabytes per second of throughput
and a maximum module size of 32 gigabytes per module.
Whereas DDR5 has a throughput of 38.4
to 51.2 gigabytes per second,
and a maximum module size of 128 gigabytes.
Now I know I just gave you a lot of different numbers
and you're probably wondering,
do I have to memorize all these different speeds?
And the answer is no.
For the exam, you are not going to be asked
how fast a DDR3 or DDR4 or DDR5 is in terms of throughput.
But if you see in a test question,
something written as PC4-16000,
you should be able to know that that means
that is 16,000 megabytes per second
or 16 gigabytes per second, and it's a DDR4 module.
Another example of this might be PC5-42000.
And this tells you it is a DDR5 module
that's running at 42,000 megabytes per second
or 42 gigabytes per second.
When it comes to memory modules,
remember, you must buy the memory module
that is appropriate for your motherboard
in terms of speed and keying.
You can't put a DDR3 into a DDR5 slot and vice versa.
Each one is keyed differently
so they won't fit into the other's slot.
Another thing to keep in mind
is that it is possible for you to mix and match modules
of the same type that have a different speed.
For example, if I have two DDR5 modules,
one at 38.4 gigabytes per second,
and one at 51.2 gigabytes per second,
and I put them both into this motherboard.
Yes, they would both fit
because this motherboard supports DDR5
and the slot is the same,
but because they transfer at different speeds,
the motherboard is going to communicate
at the slower speed to both modules.
So you ended up paying more money for a faster module,
but you're not getting that speed increase
because it's having to lower itself down
to the slower module and match that speed.
So it's always a good idea to buy modules in pairs
if you're going to use multiple modules.
So you're using the same brand,
the same speed and the same throughput in a given system.
Now, the final thing we need to talk about
when it comes to modules is the size of the modules.
If you look at a DDR3, DDR4, or DDR5 module,
they're actually pretty long,
they're about the size of your hand
from your wrist to your fingertips.
But if you're using something like a laptop
or an all-in-one unit,
you can't fit that larger module into those systems.
So there was something created known as SODIMM.
SODIMM stands for the Small Outline
Dual In-line Memory Module.
Now, SODIMM modules are still going to be classified
as DDR3, DDR4 or DDR5.
The only difference is you're also going to include
the term SODIMM in front of their name.
So you might have something like SODIMM PC4-16000.
And this tells me that this is a DDR4 SODIMM module
that operates at 16,000 megabytes per second
or 16 gigabytes per second of throughput.
Now, when it comes to installing a SODIMM module
into a motherboard, you're going to do this
by inserting it into the slot at a 45 degree angle,
and then you'll push it down flat against the motherboard
and it will be locked into place using retaining clips.
When you're using a standard desktop module
of DDR3, DDR4, or DDR5,
you're instead going to insert the module
straight in from the top
at a 90 degree angle to the motherboard
and push it into place until it clicks
and then use the retaining pins to hold it in place.
As a technician, one of the easiest things you can do
to improve the performance of a system
is to install additional memory,
taking the system from eight to 16, 16 to 32,
or 32 to 64 gigabytes of RAM,
and this can drastically improve
the performance of your system.