What is a Computer Motherboard?

What is its function?

The computer motherboard is the main printed circuit board (PCB) in the computer and is sometimes referred to as the system board, mainboard and, in Apple's terminology, the logic board.

Sometimes it's casually referred to as 'mobo'. Click here to view some computer motherboards.

The motherboard itself is just a piece of fiberglass. It's actually the hardware mounted on it that does all the work in the computer.

The motherboard connects directly or indirectly to every other part of the computer.

Its dimensions vary depending on its form factor.

There are fine copper traces etched onto the board which forms the bus.

The bus carries power and information between the components on the motherboard.

Numerous tiny holes are drilled in the bus on the computer motherboard into which chips, sockets and other electronic components are installed. Click here to view some Motherboards.

These electronic components are held in place by soldered joints on the underside of the board.

There are also other holes drilled into the motherboard to accept spacers and screws for securing the motherboard to the case.

Most computer motherboards produced today are designed for IBM-compatible PCs and currently account for approximately 90% of global computer sales.

The evolution of the mainboard has caused more devices to be integrated into it.

A typical PC has its processor main memory and other important components connected to the mainboard.

One very important component of the computer motherboard is the chipset that supports the CPU. The chipset provides support between the CPU and the various buses and external components. The chipset also controls the features and capabilities of the motherboard.

Modern computer motherboards have these basic parts

  • Chipset that forms an interface between the processor's front-side bus (FSB), main memory (RAM) and peripheral buses.

  • Sockets(slots) into which one or more CPUs can be installed.

  • M.2 Connector was previously called the Next Generation Form Factor (NGFF). It is a specification for internal mounted computer expansion card and connectors. It replaced the mSATA specifications that used the PCI Express Mini Card connections and layout. The purpose for this connector was to enhance storage speeds.

  • Non-volatile memory chips that contain the system's BIOS.

  • A clock generator that produces the system clock signal to synchronize the different components.

  • Expansion slots into which components such as video cards, sound cards, NICs, etc. are installed.

  • Power connectors that distribute power from the PSU to different components such as CPU, chipset, memory (RAM), expansion cards, etc.

Above are listed the key components of a computer motherboard. There are others that will follow.

The components of the computer motherboard such as RAM and CPU that are more subject to change, have been integrated into sockets so that they can be easily removed and replaced for upgrading.

The form factor determines the size and shape of the mainboard and also dictates what kind of case it will fit into.

Listed below are the different types of form factors.

  • Mini-ITX - This is a small form factor (SFF) board with dimensions 17 cm. x 17 cm.

  • ATX - This design improved upon the very old Baby-AT and the LPX designs. Its physical dimensions are approximaely 12" x 9.6". This design is not compatible with AT designs because the motherboard is turned sideways in the case and has a different power supply connector.

  • Micro ATX - This is a smaller version of the ATX form factor. Its physical dimensions are approximately 9.6 in. x 9.6 in.

  • XL-ATX - This is a hybrid of the ATX form factor and its dimensions are 12.8 in. x 9.6 in.

All form factors that preceded the ATX are now obsolete. A new form factor called BTX came by but disappeared quickly.

NOTE: Today, the ATX is the most popular design of the newer motherboards and it is easily upgradeable.

Computer motherboard designs are constantly changing. Listed below is a continuation of the other components of the motherboard:

Another important component is the basic input/output system (BIOS) chip which contains startup programs such as the power on self-test (POST) and drivers of the computer.

This chip controls communication between the system's hardware and operating system. BIOS can also be referred to as firmware.

Unified Extensible Firmware Interface is a specification for the software program that connects a computer's firmware to its operating system (OS). UEFI has almost replaced BIOS.

Similar to BIOS, it is installed when the computer is built and is the first program that runs when the PC is just turned on.

Intel plans to replace BIOS with UEFI by approximately 2020.

Expansion Slots:
Expansion slots enable the CPU to communicate with the peripheral devices which expand the capability of the computer.

Different cards can be plugged into these slots to enhance the computer such as video cards to improve graphics and sound cards to provide better audio.

This battery is referred to as CMOS battery and is responsible for keeping the time and date. It usually has a life span of about 3 to 4 years.

In a computer system, the CPU needs information and instructions to perform properly. This information and instructions for the CPU are stored in Random Access Memory (RAM). This memory is volatile and is referred to as Primary Memory or Main Memory.

Ports allow external devices to be connected to the computer motherboard. There are different types of ports located on the motherboard such as parallel, serial, universal serial bus (USB) and SCSI (small computer system interface).

Until up to a few years ago, printers were connected to parallel ports but now they are being replaced with the faster USB port. Low speed peripherals such as modems, mice and some scanners were connected to the serial port but are now connected by USB.

USB 1.0 had a data transfer rate of approximately 12 Mbit/s. The upgrade to USB 2.0 increased the data transfer rate by 40x to approximately 480 Mbit/s.

Now there is USB 3.0 which can transfer data faster and supply more power while being backward compatible with USB 2.0. This USB 3.0 standard promises a theoretical super speed of 5 Gbit/s.

This port can connect up to 127 daisy-chained devices all at once.

Power Connector:
Most new motherboards now come with a 24-pin connector. Older motherboards with 20-pin connectors can still be used with a 24-pin power supply since this 24-pin connector can be separated into 20-pin and 4-pin connectors.

Integrated Graphics and Audio:
Today, most of the motherboards manufactured include integrated graphics, audio and Gigabit LAN.

Hard Drive Data Transfer Modes-(Interface):
Motherboards are designed to provide different data transfer rates. Very old computers used the UDMA/33 interface but this was increased to UDMA/66 which doubled the data-transfer rate.

The data transfer rate of a hard drive is the time used to read/write information. This interface mode was upgraded to UDMA/100 and then finally to UDMA/133.

These characteristics apply to Parallel ATA hard drives. For a long time, the UDMA/133 remained the fastest interface until the inception of the Serial ATA (SATA Rev 1.0) drive which has a data transfer rate of 1.5 Gbit/s. These have now improved to SATA Rev. 2.0 with data transfer rates of 3.0 GB/s and finally SATA Rev. 3.0 with data transfer rates of 6.0 GB/s.

The addition of this socket greatly adds extra fast data transfer rates capabilities.

SATA 3 has a theoretical maximum throughput of 750 MB/s and an actual maximum throughput of 600 MB/s.

PCI-E 2.0 x2 has a theoretical maximum throughput of 1.0 GB/s and an actual maximum throughput 800 MB/s.

PCI-E 2.0 x4 has a theoretical maximum throughput of 2.0 GB/s and an actual maximum throughput of 1.6 GB/s.

Finally, PCI-E 3.0 x4 has a theoretical maxmum throughput of 4.0 GB/s and actual maximum output of 3.9 GB/s.

These hard drives can be operated in different modes called RAID (Redundant Array of Independent Disks). RAID requires more than one hard drive.

This provides speed by writing/reading information to more than one drive simultaneously - called 'striping' (RAID, 0).

Another feature is data security or 'mirroring' which duplicates data on both hard drives (RAID, 1).


A computer motherboard allows the different components of your computer system to interact with each other. It must support your choice of CPU.

Your selection of a motherboard must also be dependent on the computer system that you choose.

Click here to view other pages relating to computer mother examination and computer motherboard installation.

Click here If you would like to learn to Build Your Own Cheap Computer using Cheap Computer Parts.

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