The motherboard is the essentially the backbone of a computer, providing connectivity between all the components. All computer components plug into the motherboard in one way or another. With the demand for computer power always increasing, vendors have had to adapt motherboards accordingly. New processors, bus speeds, RAM types, data transfer speeds, and components have together pushed the evolution of the motherboard forward at a steady pace.
With all of this change, it's very difficult to keep track of the different motherboard types you'll encounter when you crack the case on your computer. This article will help you understand the differences.
Overview of motherboards
All motherboards contain similar essential components including processor slots, expansion buses, RAM banks, integrated controllers (either IDE or SCSI), power connectors, and peripheral connectors. It is these essential components that work together to provide the connectivity and communication within the computer.
Although all motherboards have similar components they are based on different form factors and when it comes to motherboards, you need to be familiar with these form factors. Form factors determine the specifications of a motherboard such as its size, shape, physical layout, and so on. When purchasing a new computer system, the form factor is important because you need to ensure that the motherboard fits with the case and other components.
Integrated vs. non-integrated
Motherboards are classified as either integrated or non-integrated. Integrated motherboards contain built-in components that are normally on found by adding expansion cards. For example, a motherboard might have video and network capabilities built right into the board, so you don't have to purchase a separate video card and network card. The obvious downside to this is that if the video or network component ceases to function, you will either have to replace the entire motherboard or disable the malfunctioning onboard component can damage other components on the motherboard, necessitating the replacement of the motherboard.
With non-integrated motherboards, the initial cost is higher because more individual components need to be purchased. In case of component failure, however, replacement of the entire motherboard can be avoided. Another issue that arises with non-integrated motherboards is the availability of expansion slots to support the multiple components.
In server motherboards, it is common to find integrated components such as SCSI and RAID controllers in addition to the video and network cards already mentioned. With large amounts of RAM installed in servers, combined with the fact that there is no need for enhanced video, servers often contain some integrated components. Component failure resulting in a smoked motherboard is still an issue though. To support these components, a non-integrated motherboard would require a minimum of four expansion slots, and this is the main reason components such as video and sound are integrated into the motherboard of a server.
Many motherboard manufacturers offer both types of motherboards. The specific components used in integrated motherboards vary between manufacturers, but they commonly include on-board video, audio, modem, and network adapter card. Some manufacturers will integrate all of these components; others will provide a selection.
As mentioned earlier, motherboards are classified by form factors. 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 including:
- AT/Baby AT
The following sections will outline some of the characteristics of each of the form factors listed above, starting with the AT/Baby AT.
The Advanced Technology (AT) was the original IBM form factor design, on which the processor, memory and expansion slots were all arranged in a straight line as shown in Figure A.
|AT was the original IBM form factor design.|
This posed a problem for full length expansion cards because the height of the processor interfered with proper card installation. In addition, heat dissipation from the processor sometimes caused problems for the expansion cards. The AT form factor also caused problems with the drive bays. The width of the board was 12" wide and 13.8" deep which overlapped with the space required for drive bays.
The Baby AT was a smaller version of the AT, only 9" wide and 13" deep, with newer, smaller components. It was a more compact board, but had the same drawbacks as the AT. In a home PC this is rarely an issue. However, in servers, many expansion cards are full length. Traditionally servers are not designed around the Baby AT form factor.
As motherboards have evolved over the years, the AT/Baby AT form factors have become obsolete.
The ATX form factor was designed to overcome the problems associated with the AT/Baby AT form factors. As shown in Figure B, the ATX component layout is different from the AT. In the ATX form factor, 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.
|The ATX form factor is different than that of the AT/Baby AT form factor|
ATX motherboards also offer advanced power management features that make them ever more attractive to computer builders. For example, ATX motherboards offer a soft shutdown option, allowing the operating system to completely power down the computer without the user's 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, is 11.2" wide and 8.2" deep.
The MicroATX, introduced by Intel in 1997, 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 often used in lower-cost systems.
The FlexATX form factor was released by Intel as an addition to the MicroATX. This form factor, which is smaller than the MicroATX, is designed for lower-end, smaller, consumer orientated systems. Some FlexATX boards do not even include expansion slots which mean expansion is only possible through USB or firewire ports.
The LPX form factor is not a standard one but a non-standard proprietary one sometimes found in desktop computer models (as opposed to towers or mini towers). 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 built-in. However, due in part to the fact that the form factor is non-standardized, the ATX form factor is more popular.
Balanced Technology Extended (BTX) form factor was released in 2003 by Intel. Unlike other form factors, this one did not evolve from an older form factor. Instead, it was a completely new form factor.
As shown in Figure C, 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.
|Balanced Technology Extended (BTX) form factor was released in 2003 by Intel.|
The three motherboards included in the BTX form factor are outlined below.
- PicoBTX - This is the smallest BTX motherboard form factor. It uses four mounting holes and one expansion slot.
- microBTX - This form factor is slightly smaller than the regular BTX but larger than the PicoBTX. It uses seven mounting holes and four expansion slots.
- BTX - Also referred to as regularBTX, is the largest BTX form factor. It uses up to ten mounting holes and supports a maximum of seven expansion slots.
NLX has been a form factor in use with desktops for quite some time. It is a compact form factor, often referred to as a "low-profile application". NLX motherboards are easily distinguished by the riser card to which the expansion cards connect. The riser cards allow from 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.
Table A summarizes the form factors outlined above, including what they are typically used for and the maximum number of slots.
Other form factors
Beyond these principle form factors, some companies have created their own motherboard layouts. For the manufacturer, this proprietary design allows for specific and custom creation of servers. For the end user or technician, however, it can be a nightmare, often requiring special training by the manufacturer before the custom equipment can be serviced. There is also the possible difficulty of locating the specialty parts.