Motherboard Expansion Slots and Bus Speeds – CompTIA A+ 220-801: 1.2


If you’ve ever looked at a
motherboard in detail, it looks like a city that you would
see if you were flying over in an airplane
from 30,000 feet. There’s a whole set of pathways
and routes, just like you would have streets
going through. There’s quite a lot of
interactions between all of these different components
on the motherboard. You will also see that there’s
a lot of places where the traffic will flow between
adapter cards and maybe flowing up to a Northbridge
or a Southbridge. And all of these separate,
independent pathways are there. It’s difficult to see
in this picture. But if you look very close at a
motherboard, you’ll see all these little traces on the
motherboard where all of that data is flowing. You also have the option on
these motherboards to be able to expand the capabilities. There are expansion slots
built right into the motherboard. So if you wanted to add
additional interfaces, some additional video options, you
can do that right with the existing hardware that you
own in that motherboard. If you look at that motherboard
carefully, you can see the bus that’s on the
motherboard itself. Sometimes these are a lot of
tiny little roads, these tiny little traces. Sometimes it’s many
traces that are on the motherboard itself. And as we see in older
motherboards, the wider the bus gave us more bandwidth. Well, that’s not necessarily the
case any longer and we’ll talk about that in this video. We’ll often refer to the
clock speed of the bus. That refers to how much data is
passing by every second or every time we have a clock cycle
inside of that computer. And you can see that the
expansion bus itself, it has its own clock. It’s not required to run at
the same speed of the CPU. If we were to look at the
specifications of a computer, we normally will see a clock
speed associated with the speed of that PC. And that’s usually referring to
the speed of the CPU that’s on the motherboard. But there are a lot of different
speeds that are occurring on that motherboard. The expansion bus itself
has its own clock. It doesn’t run at the same
speed as the CPU. You’ll notice that the numbers
of these speeds will be called MHz or GHz. That’s standing for megahertz
and gigahertz. If it is 1 megahertz, that is
one million cycles per second. A hertz being one cycle per
second, therefore a megahertz is a million cycles
per second. And obviously, a gigahertz
is 1,000 megahertz. So as we look at these numbers
and try to decipher just how fast something is running, we
need to understand how fast it’s running in Hertz, so that
we can make comparisons to other systems or other
computers. Another important consideration
is that the speed of the bus does not
necessarily correlate back to exactly how much data we’re
putting across that connection. In many cases, we can put a lot
of data over a connection over one single clock cycle. If you look at something
like memory, it’s a good example of that. Something like DDR3 transfers
data at 64 times the rate of the memory clock. That’s because it’s able to
transfer data in different ways for a single clock
across that link. That provides a lot
of efficiencies. So when we’re looking at the
bus itself and the speed of the clock of the bus, don’t
think that the speed itself limits the amount of data. In some cases, we can put a lot
of data across that bus in one single clock cycle. If we were to look at the
architecture of a computer, our adapter slots would be out
here connected to what we call the Southbridge. This is usually where we are
plugging in these expansion connections. The main processing of the
computer takes place at the CPU of course. And it’s the Northbridge that
connects all of this higher speed communication, for
instance between the memory and the CPU. The other systems that we’re
plugging in for our interfaces or perhaps other connections
are almost always happening down here on these PCI
adapter slots. Some differences to this might
be something like a graphics adapter slot. If you have a PCI Express or
an AGP slot, it may connect directly to the Northbridge. So there is this separation
inside of the computer where most of the time our slower
devices are connected to our Southbridge and the high-speed
devices are connected to the Northbridge. It’s pretty obvious when you
look at a motherboard where the expansion slots are. There’s these long slots that we
built so that we’re able to add different capabilities. It makes it very simple. If we wanted to plug in
an adapter card, we find one that matches. This happens to be a 64-bit
adapter card, into this PCI slot. We line it up with the
connectors on the slot. And we push it right into the
slot so that it goes all the way in, so that almost
none of those copper connectors are visible. When you have it in there,
you’ll see that it goes in almost completely into
that connection. So it’s very simple. You power off your computer. You plug in whatever expansion
you would like. You power it back on. And now, you have additional
capabilities available, all by adding different connectors
into those slots. PCI stands for Peripheral
Component Interconnect. That’s a mouthful. That’s why we almost always
call it a PCI slot. It was created in 1994. It’s been around a long time. And it’s so standardized that
even the newest motherboards tend to put one or two PCI slots
on there just so it’s backward compatible with your
older adapter cards. You’ll find those 32-bit
and 64-bit versions of the PCI slot. And depending on what version
of PCI happens to be running on your motherboard, you’ll
have different kinds of throughput. For instance, a 133 megabytes
per second is one that you will see on a 32-bit
PCI slot that’s running at 33 megahertz. The highest will be 533
megabytes per second. And you’re only going to get
that if you’re running with the 64-bit PCI card
at the higher clock rate of 66 megahertz. A 32-bit PCI bus is one where
we have expansion slots. We would plug in our
adapter cards. And they’re connecting over
this 32-bit bus to the Southbridge. If this was a 64-bit PCI
connection, it has twice as many connections going between
a much larger expansion slot and also connecting back
to the Southbridge. Here’s a picture of
the PCI slot. You can see the 32-bit PCI slot
is much shorter than the 64-bit PCI slot that
you’ll find. It has all these little
keys on it as well. Notice that each slot is
very different looking. And that’s because there are
these little sections on the card, these notches that are
on the adapter card itself, that both designate the size of
the card, along with what voltages are required to use
that particular adapter card. You can see this card
has a notch at the 3.3V and the 5V position. And if either of those voltages
are available on your motherboard, this particular
card will take advantage of them. The 64-bit expansion card,
much longer you can see. There’s a notch in it that
designates where that’s 64-bit happens to be. This is another adapter
card that will work in both 3.3V and 5V. But if your motherboard doesn’t
support one of those voltages, that key space won’t
be available and you won’t be able to push that card
into the motherboard. As we became more mobile, we
needed a way to take the same functionality as PCI
and shrink it down for our mobile devices. So a new standard was created
called mini PCI. This had the same type of
signaling, the same type of capabilities as PCI, but it put
it into a very, very small form factor that worked
perfectly for laptops. So we could add a Wi-Fi card,
a mobile broadband card, and put it right into the laptop
itself, but using a same standard as something that we
were very comfortable with, with the PCI format. Unfortunately, when you plug
these into the laptops, they are inside under the covers
of the laptop. So unlike a where you could plug
into an interface on a PCI adapter card, these
particular adapter cards are inside of your laptop. You really don’t have access to
it once you install it into the system. Here’s an example of what
I mean by that. This is a mini PCI card. This is a Wi-Fi card that we
put inside of a laptop. The cover has been removed. And it’s one that gives
you access. You can snap it into the slot
and then put the cover right on top of it. You see there’s a modem
connection here. There’s a slot for some
additional memory if you wanted to put it into
this laptop. Once you install the card, and
this one happens to need an interface for an antenna, so
we’ll plug in the antenna connection to this. And now, we’ve got this entire
system ready to go for this Intel wireless card. We put the cover back on. And now when we start up our
operating system, we have a brand new wireless card
available for us. One of the things we found with
PCI is as the years went on, it became much harder to get
higher throughputs through those particular legacy
interfaces. So we created an update to the
PCI called the PCI-X. That stands for PCI eXtended. We really created this for
servers that needed a lot of throughput. And they really got a lot of
bandwidth out of this update. They were able to get four
times the clock speed. It had a lot of abilities to
plug in gigabyte ethernet cards or high-speed storage. And you can see that the
capacity, the throughput of these devices, went up to 1,064
megabytes per second. Now, keep in mind this
PCI-X does not stand for PCI Express. That’s a completely different
format using a completely different method of
communication. PCI-X stands for PCI eXtended,
which is simply a newer version, an updated version
of the PCI standard. On newer motherboards these
days, you’re going to find PCI Express slots. You’ll see that abbreviated as
PCIe, with a lowercase “e.” It’s important to delineate the
difference between that PCI-X format and the newer and
certainly much more common, PCI Express. If you look at a new motherboard
these days, they almost always are going to be
primarily a PCI Express bus that you’ll see on
that device. You will also see this
abbreviated as PCIe with that lowercase e. This is not the PCI-X for
the abbreviation. PCI Express is PCIe. PCI Express also is not
that traditional 32 or 64-bit wide bus. With PCI Express, we’re using a
serial communication to send traffic in both directions. We call these lanes. What’s nice about this is that
we can plug in a very slow PCI Express card and we can plug
in a very high speed PCI Express card and they’re using
their own lanes to communicate. In the older PCI style, if you
plugged in a slower card, the entire bus had to slow
down to that speed. We don’t have that problem
with PCI Express. You’ll see the size of these
adapter connections for PCI Express as 1, 2, 4, 8, 16,
or 32 full duplex lanes. And you’ll see them written
as x1, x2, x4. And the x here is pronounced
“by.” so you’ll see a “by 1,” a “by 4,” a “by 16,” and a lot
of different interfaces. And they all have different
sizes as well. Sometimes it’s very easy to
pick out the difference between a by 1 interface
and a by 16 interface. PCI Express doesn’t have all of
those separate wires and a parallel communication. It’s simply has a single lane. So a Express by 1 slot is going
to have a connection up to the Northbridge. Because we’re using a much
faster communication here, we generally connect to
the Northbridge. And there’s another lane
on the way back. So this is a full duplex
communication, going back and forth to that Northbridge. If we need more throughput,
let’s say we’re putting in an adapter card or a device that
needs more speed, we can simply plug it into a slot that
has got more connections, more lanes of communication. So a by 4 slot is going to have
four of those full duplex lanes between the interface
card and the Northbridge. Through the years, there have
been different versions of PCI Express that we’ve seen. And you’ll need to look at your
motherboard to determine what version of PCI Express
it happens to be using. If we wanted to compare the
different speeds between those different versions, you can see
that version 1.x had 250 megabyte per second lanes
in each direction. When we got to PCI Express
version 2.x, it doubled the speed up to 500 megabytes. per second. Although you don’t see it very
often, there is a standard version 3.0 and it has the
capability of sending 1 gigabyte per second in
either direction. And there is currently under
way work for version 4.0. And it is said to increase the
speed up to 2 gigabytes per second in both direction, when
you’re working in a PCI Express environment. When you look at a motherboard
that has PCI Express slots, you’ll see different sizes of
the slots depending on the number of lanes they’re using. This motherboard also has some
of the legacy PCI connectors. And here’s a PCI Express
by 16 slot. Here’s another by 16 slot. You can see they’re very long,
especially when you compare them to the PCI by 1 slot. Those are relatively short,
very small connections. You don’t need a lot
of real estate. There’s only two lanes there
that you’re going to use, really one lane,
bidirectional. You’ve got that full duplex
connection in that by 1 slot. If you were to look at the
adapter cards for that, they match this. For instance, here’s an adapter
card that is a PCI Express by 1 adapter card. And you can see it doesn’t
take up a lot of room. That serial communication really
allows you to very efficiently transfer information
between the adapter card and the
motherboard. Another legacy interface you
might run into is the CNR. That stands for Communications
and Networking Riser. This was created just so we
could add additional network cards or additional modems
into our computers. This is a very, very
small interface. It’s the small yellow interface
here at the bottom. And it was designed just
for this purpose. The idea being on most systems,
you really didn’t need very much. There’s so much already
integrated onto the motherboard, that we just need
an additional slot that was able to perform these particular
functions. Well these days of course,
motherboards have almost everything included on them. So we don’t often see a
CNR slot on our modern motherboards. Another legacy slot you might
run into is the AGP slot. This stands for Accelerated
Graphics Port. We almost always call it AGP. And you’ll see it written on
the motherboard with the letters AGP next to
the slot itself. Before we had PCI Express, we
needed some way to increase the throughput for
our video cards. There was a lot of gaming, a lot
of high-end graphics that was required. And AGP was built
just for that. So we were always able to plug
in and get some additional video out of these AGP slots. But now that PCI Express is
around, we have much more bandwidth available. Almost all of the new video
cards that we see are using PCI Express as its slot. If you compared a PCI card with
AGP, you’d see there’s a lot more connectors
on that AGP card. There’s a lot more throughput
that we needed. Therefore, we needed more
connectors to the motherboard. Many of these cards also have
these notches on them that allow you to lock that
particular card into a section of the motherboard. That way if the workstation is
jostled or moved, you can be assured that that card isn’t
accidentally going to pop out of the slot. As AGP matured, we also got
higher throughputs out of AGP. The initial versions, version
1.0, which ran at 3.3 V, gave us what we call an AGP 1x and 2x
speeds that give the speeds up to 522 megabytes
per second. The next version
of AGP, version 2.0, was a 1.5V version. But you can see, it was a 4x,
which means we were able to get 1.07 gigabytes per second
out of that standard. And you can see, we doubled it
again with AGP 8x to 2.1 gigabytes per second. We were able to get a
lot of throughput through that AGP 8x. You can also see in that 3.0
version that we had an 0.8V as the standard on that bus. As time went on, we got very
efficient with using the power on AGP. And you can see as we went
through the different versions, the bus requirements
itself dropped from a 3.3V all the way down to 0.8V. Just like all of the
other expansion slots, AGP is very unique. You can’t plug PCI into AGP and
vice versa because of the format of the slot itself. And most of the time, you’ll see
on the motherboard that it specifically says that’s an AGP
connection, so you can be very sure what your plugging
into and how you’re connecting to that motherboard. You can see there have been a
lot of different interface types through the years. And all of these buses allowed
us to improve the capabilities of our computers. And if you look at your desktop,
you’ve probably got one or two of these available
so that you can add on additional capabilities
to your computer.

32 thoughts on “Motherboard Expansion Slots and Bus Speeds – CompTIA A+ 220-801: 1.2

  1. This guys pretty good, the way he starts off the material is what you should be learning… Check out his 701 stuff which is still valid and you'll see the way he outlines the course.

  2. I know I'm not Professormesser, but the answer to your question is that the southbridge is sort of like a handler for the slower I/O devices and it delivers that data to the northbridge. At the same time, the northbridge handles the higher speed I/O devices and delivers the data to the CPU via the Front Side Bus. The primary data that the northbridge handles is the "more important" information that needs an extremely fast highway to get to the CPU, but it also handles slower information as well.

  3. Bravo Sir you just saved me about 30 mins of reading and I believe my intake of information was much better than if I just read it.

  4. Writing my 801 exam tomorrow, most of the exam is about pc hardware. Thank you for the way you explain everything in a easy to understand manner.

  5. how did you do? Does the exam really grill us on very specific things, like, say, the speed of PCIe x16 vs PCI-X?

  6. @Nabakaron I believe it is simply due to cost and the fact that PCI has been around a while longer, so naturally they didn't want to automatically put everyone's adapter cards into obsoleteness. But that is use my own personal guess on the subject.

  7. I just wanted to say thank you for putting this together…it is helping me understand how everything works and why it works

  8. thanks Professor Messer for taking time to put these videos together, if has help me to understand the whole operations of computer. I know basic usage for computer but in order to fulfill my dream of being A+ certified , I am gaining a better understanding.  Reading the book and still not understanding doesn't help.  So much to study, was overwhelm with where and what to study. you help to put things in some order.  THANKS SO MUCH!!!!!!!!!!!!!!!!!!!!!

  9. These videos are great even fantastic study options but to be totally prepared I dont think theres any one single thing that will prepare you left by itself. Best preperation is to use many diferent study options. Good Luck studying!!! It pays off in the end if you work hard at understanding the material.

  10. I've just finished another course on A+ and have come to learn some more from your great videos and service! First . . thank you!

    I have a question though, when you refer to the speed, to you actually mean BITES, or do you mean BITS? Everything I've learned so far has pointed toward "b" instead of "B," and . . . well there's quite a gap of speed there if we're transferring 2 GB/s versus a Gb/s.

    I hope you can help me out with this question, and thank you so much in advance! 🙂

  11. This video makes it much easier to understand. After reading about the North and South Bridge in a text book, it was hard to understand what being read. This video helps you remember where items are located on the motherboard. Thanks

  12. So if the PCIe 3.0 has a speed of 500MB/s, how does the PCIe Intel 750 SSD give the 2.2GB/s speed that it promises..? If PCIe 3.0 only has a speed of 500MB/s ? Really nice video, I'm actually going to be building my first PC, and wanted to learn as much as possible, before I buy the parts needed. I actually do know how to build a PC, but before I even touch the parts, I would like to understand as much as possible in two months as possible. (+1 : 619)

  13. i was wanting to build a dual cpu gaming rig cheap 😛 i can only ever see white and black slots. been doing alot of research but not getting anywhere. would i be able to use a gpu like the gtx 660 or would i gave to use agp or low profile. I would also like to sli 🙂 this video held the most info thanks 🙂

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