The motherboard is the main circuit board inside a computer. The important system components like the central processing unit (CPU) and random access memory (RAM) modules are connected directly to the motherboard via slots or sockets designed specifically for those components.

The motherboard will also provide a number of expansion slots designed to accommodate add-on cards such as video graphics adapter (VGA) cards and network interface cards (NICs). In this Chapter, we will understand the main features of the motherboard, types of motherboard, motherboard form factors, and various components of motherboard.

Introduction to Motherboard

The motherboard is also known as main board or system board. The motherboard connects the components of a computer and provides power to the systems that need low power.

The motherboard contains a socket in which one or more processors are attached. In addition it has slots that allow connecting peripheral cards such as video cards, sound cards, and networking cards.

Types of Motherboard

Motherboards are classified as either integrated or non-integrated.

Integrated motherboard

This has several components integrated into the board itself. These may include the video card, sound card, and various controller cards. The maintenance is of a specific nature as the repairing of the whole board is a complex task.

Non-integrated motherboard

This motherboard uses install-able components and expansion cards. In non-integrated motherboard, if any component fails, it is possible to replace that component instead of changing the entire motherboard. For example, you can remove the old video card and install a new one. Non-integrated motherboards typically have several PCI Expansion slots as well.

Basic Components of Motherboard

The modern motherboard has the following components —

• sockets (or slots) to install one or more microprocessors.
• slots to install main memory RAM.
• a chipset which forms an interface between the CPU’s frontside bus, main memory, and peripheral buses.
• non-volatile memory chips usually flash ROM in modern motherboards, containing the system’s firmware or BIOS.
• a clock generator which produces the system clock signal to synchronise the various components.
• slots for expansion cards. These interface to the system via the buses supported by the chipset.
• power connectors, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.

Motherboard Form Factors

Motherboards are classified by form factors. The form factor of motherboard refers to its overall dimensions and layout. Form factors essentially define the layout of the actual motherboard including the dimensions, component positioning, mounting holes, number of expansion slots, and so on. There are several different types of form factors as explained below.


AT (Advanced Technology) form factor first introduced by IBM in 1984, and used till 1997, in processors like P2 to P5 generation. Its size was 350 mm x 305 mm (13.8″ x 12″).


It works on the six pin plugs and sockets which are used to work as power connectors. The processor, memory, and expansion slots were all arranged in a straight line as shown in above Figure.

Baby AT

The smaller version of the AT form factor is known as Baby AT, introduced in 1989 and still found in computers today. The Baby AT has dimensions of 330 mm x 216 mm (13″ x 8.5″). It is also cheaper.

ATX Motherboard

The (ATX) Advanced Technology extended form factor, introduced by Intel in 1995, was designed to overcome issues with the Baby AT. In ATX, the processor and memory are arranged at a right angle to the expansion slots, allowing room for the use of full length expansion cards. In the newer computers, the combined height of the processor, heat sink, and cooling fan make it possible to insert full length cards in any other form factor, and most new computers, including servers, are built around the ATX form factor.

ATX motherboards also offer advanced power management features that make them ever more attractive to computer manufacturers. For example, ATX motherboards offer a soft shutdown option, allowing the operating system to completely power down the computer without the user having to press the power switch. A full size ATX board is 12″ wide and 9.6″ deep. There is also a smaller version referred to as the Mini-ATX board that is 11.2″ wide and 8.2″ deep.


This was introduced by Intel in 1997 and is a compatible variation to the ATX board outlined above. As the name would imply, the microATX is smaller than the standard ATX board because of the reduced number of I/O slots on the board.


Due to the fact that it is smaller than the standard ATX board, the microATX form factor reduces the cost of computers and is used in lower cost systems.


A further variant of the ATX form factor called FlexATX was released by Intel in 1999, reducing the size of the motherboard to 229mm x 191mm (9″ x 7.5″) and limiting the number of expansion slots to two.


This further reduces the overall cost of the system and allows an even more compact system design, while maintaining backward compatibility with other ATX formats. The FlexATX uses the same mounting holes as its predecessors, avoiding the need to retool an existing chassis.


In an attempt to reduce the space requirements of computer systems, Western Digital introduced their proprietary Low Profile extension (LPX) form factor in the early 1990s. The LPX form factor is a non-standard proprietary one sometimes found in desktop computer models. This form factor is characterized by an expansion board that runs parallel to the motherboard.


A riser card arrangement is used for expansion cards thereby allowing for smaller cases. The disadvantage is that this limits the number of expansion cards available. LPX motherboards are typically integrated and most have the video and sound components builtin. However, due in part to the fact that the form factor is non-standardized, the ATX form factor is more popular.


The number of expansion slots was limited in LPX, the system was difficult to upgrade or repair due to its proprietary format and the low availability of compatible parts and poor airflow inside the chassis could lead to cooling problems.

The format was revised by Intel and standardized in the shape of the New Low-Profile extended (NLX) form factor in 1997. NLX motherboards are easily distinguished by the riser card to which the expansion cards connects. The riser cards allow two to four expansion cards to be plugged in. These expansion cards sit parallel to the motherboard.

Servers with this form factor offer power that is similar to the larger traditional servers but in the size of a VCR. The obvious benefit of the NLX form factor is that the bulk of a traditional server is reduced to a space saving smaller server. Additionally, servers assembled in a rack mount case can be secured to a rack which can itself be secured to the floor, providing better equipment safety.


The Balanced Technology extended (BTX) form factor was released by Intel in 2004 as the successor to the popular ATX format. It has a number of new features including changes to the layout of the board designed to improve component placement, enhancing airflow inside the case, and reducing the number of cooling fans needed.


The BTX form factor allows for more integrated onboard components because it is larger than ATX. The airflow path is optimized by moving the memory slots and expansion slots. This allows the main system board components to use the same airflow thereby requiring fewer fans and
reducing noise.

The three motherboards included in the BTX form factor are outlined below:


This is the smallest BTX motherboard form factor. It uses four mounting holes and one expansion slot.


This form factor is slightly smaller than the regular BTX but larger than the PicoBTX. It uses seven mounting holes and four expansion slots.


Also referred to as regular BTX, it is the largest BTX form factor. It uses up to ten mounting holes and supports a maximum of seven expansion slots.

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