CompTIA®A+ Exam Notes : Motherboard Components And Their Purpose


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1. PC Hardware

1.2 Motherboard Components and their purpose

The motherboard is the computer's main circuit board. It's a thin plate that holds the CPU, memory, connectors for the hard drive and optical drives, expansion cards to control the video and audio, and connections to your computer's ports (such as USB ports). The motherboard connects directly or indirectly to every part of the computer.

This motherboard was developed by intel in 1995. ATX is the most common motherboard design. Several ATX-derived designs have been specified that use the same power supply

ATX (Advanced Technology Extended) is a full size board measuring 12" wide by 9.6" deep. ATX has 6-pin mini keyboard connector. Also, it has double row single power supply connector providing +/-5V, +/-12V, and +3.3V.

MicroATX is a small motherboard size of 9.6" x 9.6". Compared to full size ATX, microATX have smaller number of I/O slots. For example, full ATX can have 5 PCI slots, whereas MicroATX can have up to 3/4 PCI stots only. The chief advantages over ATX is reduced size, and power requirements. The microATX form factor was developed as a natural evolution of the ATX form factor to address new market trends and PC technologies. The microATX form factor improves upon the previous specification in several key areas.

ITX: ITX is the smaller version of the motherboard. The user will find only a few expansion slots that are because of its small size. Also, one can find the ITX mini as well which have only one expansion slot. Since the space on this motherboard is less, so one might find very less feature son this motherboard. The mounting points which would be found by the user are same as the ones he would find in Micro ATX or the ATX. So, one can fit them one by one in the same type of case. So, many manufactures actually build the case in the way that whatever motherboard is used, it can get fit into the case. SO basically, the Mini ITX gives an edge to the user if he wants to have the motherboard which covers only a small room.

Mini-ATX motherboards were designed with Mobile on Desktop Technology which adapt mobile CPUs for lower power requirements and less heat generation. Mini-ATX motherboards use surface-mount technology and solid state capacitors.

Given below are the main differences between ATX and Micro ATX boards:

1. ATX is larger than Micro ATX

2. ATX boards typically have more expansion slots than Micro ATX boards.

3. A Micro ATX board can be installed in an ATX chassis but not the other way around.

4. A Micro ATX chassis has fewer drive bays than an ATX chassis.

5. AT style systems use two power connectors, P8 and P9 to connect to the motherboard. ATX systems use only one P1 connector to connect to the motherboard.

6. ATX is a hardware (motherboard) specification of desktop computers introduced by the Intel Corporation in 1995 as advancement from the existing AT specification.

7. MicroATX is a hardware specification introduced based on the ATX specification standard; therefore, it is compatible with the peripherals and add-on devices used for ATX computers. The power supply, I/O panel, and connectors are the same.

8. MicroATX is smaller than the standard ATX configuration. It has less expansion slots and fan headers than a standard ATX.

9. Chassis of a micro ATX is smaller, but microATX motherboard can be installed in a standard ATX board too.

The relative sizes of ATX, Micro ATX and Mini-ITX are shown below:

sizes of ATX, Micro ATX and Mini-ITX

Further, Mini ITX is limited to one PCI-e slot, and up to 2 memory slots. For most PC applications, Mini-ITX is sufficient unless you want to go for more PCI-e slots or do heavy gaming (display-intensive).


The ATX standard has two different versions of the main power cable: the original 20 pin cable, and the newer 24 pin cable. The main ATX connector is a 20-pin connector. The four pins carrying power are 3.3 V, 3.3 V, 5 V, and 5 V. This allows the motherboard to pull about 20 to 30 watts.

The 24-pin ATX connector is simply the 20-pin connector along with the extra 4-pin connector on the side. This provides the 4 pins carrying power as ATX 20-pin connector plus an additional 4 pins with 5 V standby, 12 V, 12 V, and 3.3 V. The below shows the 24-pin ATX power connector.

1. ICH9 is Intel's own 'southbridge' chipset and it stands for I/O Controller Hub 9. The northbridge and southbridge are also known as MCH (Memory Controller Hub) and ICH, respectively.

2. SPDIF, also written as S/PDIF, stands for Sony/Phillips Digital Interface, and is an interface to transmit digital audio. Among the two consumer-level interfaces to transmit audio in digital format: SPDIF and HDMI (High-Definition Multimedia Interface) . SPDIF transmits only audio, but HMDI also carries digital video signal.

3. PCIe is an updated version of the PCI protocol. PCIe cards can always operate in PCIe slots with the same or more lanes than the card. For example, an x8 card can operate in a slot with x8, x16, or x32 lanes.

4. TPM: The TPM would be mostly utilized by applications that require or are related to security, such as encryption/decryption, and authentication. Trusted Platform Module (TPM) is a microchip that is built into a computer. It is used to store cryptographic information, such as encryption keys. Information stored on the TPM can be more secure from external software attacks and physical theft.

BitLocker uses the TPM to help protect the Windows operating system and user data and helps to ensure that a computer is not tampered with, even if it is left unattended, lost, or stolen.

BitLocker can also be used without a TPM. To use BitLocker on a computer without a TPM, you must change the default behavior of the BitLocker setup wizard by using Group Policy, or configure BitLocker by using a script. When BitLocker is used without a TPM, the required encryption keys are stored on a USB flash drive that must be presented to unlock the data stored on a volume.

5. USB (Universal Serial Bus) Port: There are usually a couple of these ports located on each motherboard used for connecting pen drives and external hard drives, like Ipods or Mp3 players.

6. RJ-45 (Registered Jack 45): It is commonly used for an Ethernet or serial connection with an 8 position 8 conductor (8P8C) jack. 

7. Audio ports:

a) Line In port (light blue): This port connects a tape, CD, DVD player or other audio sources.

b) Line Out port (lime): This port connects a headphone or a speaker. In 4-channel, 6-channel, and 8- channel mode, the function of this port becomes Front Speaker Out. 

c) Microphone port (pink): This port connects a microphone.

d) Side Speaker Out port (gray): This port connects to the side speakers in an 8-channel audio configuration. 

e) Rear Speaker Out port (black): This port connects to the rear speakers on a 4-channel, 6-channel, or 8-channel audio configuration.

f) Center/Subwoofer port (yellow orange): This port connects the center/subwoofer speakers 

8. PCI Express x16 : graphics interface offers increased bandwidth and scalability over the previous AGP8X generation. PCI Express x16 allows up to 4 GB/s of peak bandwidth per direction, and up to 8 GB/s concurrent bandwidth.

9. PCI Express x4 : graphics interface allows up to 800 MB/s of peak bandwidth per direction.

10. PCI (Peripheral Component Interconnect) Slot: Supports peripherals like sound cards, DVD decoders, and graphic accelerators with 32 bits at 33Mhz capabilities. There are usually anywhere from 1 to 6 PCI slots available on the motherboard.

11. Printer Header: It is parallel port used to connect scanners and printers. 

12. COM (Communication) Port: The port designed to connect your mouse and modem.

13. IDE Connector: Responsible for connecting the IDE cord used for hard disks, CD drives, and DVD drives.

14. CPU slot: To install the CPU, just slide it straight down into the slot. Special notches in the slot make it impossible to install them incorrectly. So remember if it does not go easily, it is probably not correct. Be sure to plug in the CPU fan's power.

15. SATA Controller: Motherboard will typically have SATA controller for connecting SATA enabled devices such as Hard disks

16. CMOS (complementary metal-oxide-semiconductor): It is also called as non-volatile BIOS memory is the term usually used to describe the small amount of memory on a computer motherboard that stores the BIOS settings. The CMOS is usually powered by a CR2032 cell battery. Most CMOS batteries will last the lifetime of a motherboard (up to 10 years in most cases) but will sometimes need to be replaced. Incorrect or slow system date and time and loss of BIOS settings are major signs of a dead or dying CMOS battery. The Complementary Metal-Oxide Semiconductor (CMOS) allows the computer to store the Real Time Clock (RTC)and other device information even after the computer is switched off and on. This is achieved by using a battery just for CMOS. If you notice that the time is constantly incorrect, even after adjusting correctly, the most likely cause is that the CMOS battery has become weak and need to be replaced. 

17. 24 - pin ATX Power connector: The ATX standard has two different versions of the main power cable: the original 20 pin cable, and the newer 24 pin cable. The main ATX connector is a 20-pin connector. The four pins carrying power are 3.3 V, 3.3 V, 5 V, and 5 V. This allows the motherboard to pull about 20 to 30 watts.The 24-pin ATX connector is simply the 20-pin connector along with the extra 4-pin connector on the side. This provides the 4 pins carrying power as ATX 20-pin connector plus an additional 4 pins with 5 V standby, 12 V, 12 V, and 3.3 V. The below shows the 24-pin ATX power connector.

The CPU socket is the array of hundreds of holes or metal plates to which a computer's central processing unit connects. The CPU socket supplies power to the processor and allows data to be sent to and from the processor from the computer's memory. 

Add-on Card Connectors: Many motherboards have connectors for computer add-on cards. These connectors are long slots into which the cards are inserted. There are several types of add-on card connectors. Some of the most common include Peripheral Component Interconnect Express (PCIe) and Accelerated Graphics Port (AGP), used mainly for video cards, and conventional Peripheral Component Interconnect (PCI), used for other types of add-on cards such as sound cards and storage controllers.

RAM Slots: A memory slot, memory socket, or RAM slot is what allows computer memory (RAM) to be inserted into the computer. Depending on the motherboard, there may be two to four memory slots (sometimes more on high-end motherboards) and are what determine the type of RAM used with the computer. The most common types of RAM are SDRAM and DDR for desktop computers and SODIMM for laptop computers, each having various types and speeds. 

Chipset: North Bridge connects directly to the CPU, whereas the South Bridge is connected to the North Bridge

  • The northbridge typically handles communications among the CPU, in some cases RAM, and PCI Express (or AGP) video cards, and the southbridge.

  • The southbridge is one of the two chips in the core logic chipset on a personal computer (PC) motherboard, the other being the northbridge. The southbridge typically implements the slower capabilities of the motherboard in a northbridge/southbridge chipset computer architecture.

  • A southbridge chipset handles all of a computer's I/O functions, such as USB, audio, serial, the system BIOS, the ISA bus, the interrupt controller and the IDE channels.

Mini ITX: Various components of Mini-ITX motherboard are as shown in the below figure

Various components of Mini-ITX motherboard


SanDisk Extreme SSD, which supports SATA 6Gb/s interface and when connected to SATA 6Gb/s port, can reach up to 550/520MB/s sequential read and sequential write speed rates respectively. However, when the drive is connected to SATA 3 Gb/s port, it can reach up to 285/275MB/s sequential read and sequential write speed rates respectively.

Express Card is an interface to allow peripheral devices to be connected to a computer, usually a laptop computer. Formerly called NEWCARD, the Express Card standard specifies the design of slots built into the computer and of cards which can be inserted into Express Card slots. The cards contain electronic circuitry and connectors to which external devices can be connected. The Express Card standard replaces the PC Card (also known as PCMCIA) standards.

PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed serial computer expansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards.

NIC, Network Interface Card is the one that interfaces your PC to the LAN. NIC sits in your PC on one of the slot available on the motherboard.

  • Advanced Configuration and Power Interface (ACPI) specification provides an open standard for device configuration and power management by the operating system.

  • The specification is central to Operating System-directed configuration and Power Management (OSPM), a system implementing ACPI, which removes device management responsibilities from legacy firmware interfaces.

  • The Advanced Host Controller Interface (AHCI) is a technical standard defined by Intel that specifies the operation of Serial ATA (SATA) host bus adapters in a non-implementation-specific manner.

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