The motherboard

When we open a computer and look inside, it is inevitable to be surprised by the motherboard. The amount and variety of components can scare us a little, but in this post, we are going to analyze them and take away some basic ideas that will help us in our understanding of motherboards. In any event, first thing is to understand what the motherboard is and what it is for.

The motherboard
The motherboard

The motherboard is the integrated circuit that connects all the components of the computer. Some of them will be directly soldered to the plate. Others, such as the CPU or RAM, are connected through dedicated connectors. And the rest they do it through the so-called expansion buses (internal ports) or through the external ports.

Everything ends up connecting to the motherboard, either by cable or by radio. A Wifi printer also connects to the motherboard, it is the only way it has to be accessible to the CPU.

The components that are connected, can be from different manufacturers and the motherboard has to be able to connect all of them. Then, it is necessary to stablish a series of guidelines to ensure the correct connection of all components.

The number of standards is many and they are defined by a lot of factors: physical dimensions, electrical characteristics or communication protocols, to name a few.

Form factor

To differentiate the different motherboard standards, we are going to look at the so-called form factor. This is a very basic standard that mainly defines the shape (square or rectangular) of the motherboard, some physical characteristics and connectors.

This way, if we have a motherboard of a certain form factor, we can only connect a power supply of the same form factor.

There are several form factors, although they can be group into two that have a series of variants:

  • AT factor: It is the oldest and assumed a very large board size, they were also designed for text environments, so we could connect the keyboard, but there was no mouse connector. Needless to say, these plates are totally obsolete and today you do not find them on any computer, so we will not talk more about them in the rest of the post.
  • ATX Factor: They are the smaller modern boards with more connectors. We can find many variations of these, among which some characteristics change, but the operation and components are practically the same, so in this post I will give an overview. Anyway, if someone were interested they can find a lot of information on the Internet.

In class, to let my students know that the form factors are many, I usually use the following image:

Form factors
Form factors

Even for these form factors there are more variations, as the case of DTX, for which you can find: DTX, Mini DTX and Full DTX.

Proprietary motherboards

There are also the so-called proprietary motherboards, which do not follow the standards but proprietary specifications of the manufacturer of the board, which means that only specific components of the manufacturer or other manufacturers that have an agreement with the first one can be connected. DELL is one of the companies that has been manufacturing this type of motherboards.

Motherboard components

The motherboard is a plate that holds a bunch of integrated circuits and connectors. Certainly, identifying all the components of a motherboard is a little scary. If you don’t believe me, take a look at this image taken from the instructions of a motherboard:

Motherboard components
Motherboard components

It imposes, doesn’t it? That is why I hasten to tell my students that they do not have to know the operation of the entire motherboard, after all, they are not going to dedicate themselves to its design or manufacture. I’m happy if they are able to identify the main components that we can see on it when we open a computer. My impression is that I do not reassure them much, but in a later class doing a workshop where students open some computers, they finally realize that they are able to identify those components by themselves.

In this section, we are going to take a tour of the most important components that I understand we have to be able to identify. We will use an ATX form factor board. My list of components to identify is:

  • CPU connectors: Socket and fan power connector.
  • RAM slots
  • Power Supply Connector
  • EIDE and Serial ATA ports
  • Chipset: Northbridge y Southbridge
  • Expansion slots
  • BIOS
  • DIP bridges and switches
  • Time and date battery
  • External ports

CPU connectors

In early computers, the CPU was directly soldered to the motherboard and carried no fan, so it was visible and easily and quickly identifiable. However, with the evolution of CPUs, they got more and more contacts, and it became more convenient not to solder it directly to the motherboard but use a special type of connector, the CPU socket. In addition, they were increasingly faster and had a higher level of integration, which caused them to generate more heat, increasing the dissipation requirements.

This new need was solved by adding a heat dissipation system to the CPU. Nowadays, you do not see the CPU when you open the computer, they have a heatsink and a fan that cover them.  The heatsink is in direct contact with the CPU through a thermal conductive gel, to favor the transfer of heat from it to the heatsink. We would see something like this:

CPU with heatsink and fan
CPU with heatsink and fan

As I already mentioned, the CPU is not directly soldered to the motherboard, but connects to a connector that is soldered to it. I leave you an image in which you can appreciate a CPU socket and the back of the CPU with all the pins that fit into the socket. I imagine that with this picture you can get a good idea of how it is connected:

CPU and its socket
CPU and its Socket

Of all this structure, the component of the motherboard is the socket of the CPU, the rest are components that do not belong to the motherboard, but connect to it.

I imagine that you are thinking that this makes us able to change the CPU of a motherboard, since it does not come soldered to it. Well, yes, that’s the way it is. Although we will always have to choose a new CPU compatible with the motherboard.

Additionally, the CPU fan requires a connector for powering. This can usually be easily located because it will be labeled with FAN1

CPU Fan connector
CPU Fan connector

RAM slots

RAM memory is another element that we have to connect to the motherboard so that the CPU can communicate with it. The motherboards have a series of slots with a kind of pins that are used to hold the RAM memories. They will be located very close to the CPU to facilitate communication.

There are different RAM slots formats, with different numbers of connectors called pins, depending on the type of the RAM memory.  I will go through them in detail when I explain the RAM in another post.

RAM slots
RAM slots

Power supply connector

It is the connector used to connect the power supply to the motherboard and that way, be able to provide power to all the elements of the motherboard. Like all connectors, the power supply connector has evolved over time. Nowadays, on modern motherboards you will find the ATX connector:

ATX connector
ATX connector

We can also find the EPS connectors that provide an additional 12 volts:

EPS connector
EPS connector

In a later post, I will talk about the power supply and I will show the evolution of the connectors of that to the motherboard, as well as the rest of the connectors used to supply power directly to other components, as could be the case of the hard disk.

EIDE and Serial ATA ports

For the connection of internal devices, hard drives and CD-ROM drives, we can usually find two types of connections: The EIDE port and the Serial ATA port. Here are some images of both:

EIDE and Serial ATA
EIDE and Serial ATA

This is the most common, but there are other types of connectors, such as SCSI (Small Computer System Interface) or FDD (Floppy Disk Drive). The last one in total disuse, since flash memories have completely replaced flexible external disks.

Chipset

The chipset is a group of chips that helps the CPU in its communications with the rest of the components, freeing it from this work. It acts as the communications center and traffic controller of the motherboard, and ultimately determines which components are compatible with the motherboard, including CPU, RAM, hard drives, and graphics cards.

Chip Northbridge: used by the CPU as a mediator in communications with RAM. This chip generates a lot of heat due to the intense work it does, so it has its own heatsink and, in some cases, also a fan.

Chip Northbridge
Chip Northbridge

Chip Southbridge: acts as a mediator in communication with some expansion devices and mass storage drives: hard drives and floppy disks.

Chip Southbridge
Chip Southbridge

I will talk about the CPU, in other post, and how it communicates with the rest of the components. Then, I will explain the operation of the Chipset and its function of supporting the CPU, but at this point, our goal is to be able to identify them on the motherboard.

Expansion slots

Apart from the CPU, RAM memory and other storage systems, the motherboard also has to connect other elements such as the graphics card or a hard drive, to name a few. With that purpose, the expansion slots were designed to connect a set of different components to the motherboard, and we have to be able to identify them on the motherboard.

Expansion slots have evolved a lot and if we look at the history of them I would have to present a long list of them. Among the oldest slots that are already obsolete, I highlight: ISA, MCA, EISA and VESA. Which I will not explain, because you will not find them unless you work with very old motherboards.

I will focus on three expansion slots:

PCI: (Peripheral Component Interconnect): They are general purpose slots, used by a wide range of expansion cards. For example, they can used by a Modem card, a sound card, etc.

AGP (Accelerated Graphics Port): They are usually the ones that are closest to the Northbridge, and are used to connect video cards.

CNR (Communications and Networking Riser): Used for network and modem cards

Here I leave an image with all of them:

Expansion slots

The BIOS

Motherboards have a set of codes that indicate to the CPU how to communicate with the different devices connected to the motherboard. These programming codes form the basic system of inputs and outputs, known as BIOS, and they are stored on a chip known as the Flash ROM.

BIOS
Chip BIOS

DIP switches and bridges

On motherboards, we can find a number of switches that are used to make changes to the board configuration. For example, to adjust the clock speed of the motherboard.

DIP switches and bridges
DIP switches and bridges

Date and time battery

Most motherboards incorporate a battery that allows date and time settings to be maintained with the computer turned off.

Date and time battery
Date and time battery

External ports

Motherboards have a number of ports that are accessible from the outside, without the need to open the computer case. These ports are used to connect a multitude of peripherals.

Here you have a picture showing many of them:

External ports
External ports

Well, and with this I have finished the list of components that I intend for my students to be able to identify when opening a computer and seeing the motherboard.

NOTE:

This post is part of the collection “Computer Architecture” that reproduces my class notes. You can see the index of this collection here.

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