The form factor of a motherboard determines the specifications for its general shape and size. It also specifies what type of case and power supply will be supported, the placement of mounting holes and the physical layout and organization of the motherboard.
Form factor is especially important if you build your own computer systems because you must buy the correct case and components that will fit the board.
Today, the most common form factors are ATX and Micro ATX although BTX has gained some ground.
So that motherboards can be built to fit different brands of cases, quite a few standards have been developed over the years:
The AT form factor is found in older computers (386 class or earlier). Some of the problems with the AT form factor arose because of the physical size of the motherboard, which was 12" wide. This often caused the motherboard to overlap the space that was needed by the drive bays.
Following the AT form factor, the Baby AT form factor was introduced. With the Baby AT form factor the width of the motherboard was decreased from 12" to 8.5", limiting problems associated with overlapping. Baby AT became popular and was designed for peripheral devices - such as the keyboard, mouse and video - to be contained on circuit boards that were connected to expansion slots on the board.
Baby AT was not without its problems. Computer memory itself advanced, and the Baby AT form factor had memory sockets at the front of the motherboard. As processors became larger, the Baby AT form factor did not allow for space to use a combination of processor, heat sink, and fan.
The ATX form factor was designed to overcome these issues.
The ATX format is an upgrade to Baby-AT. It was intended to improve ease of use. The connection device on an ATX motherboard is designed to make plugging in peripherals as easy as possible (for example, the drive connectors are located beside the disks.) What's more, motherboard components are arranged in parallel, to improve heat removal and air circulation. It also made it easier to access the many components that make up a PC.
Some of the design specification improvements of the ATX form factor included a single 20-pin connector for the power supply, a power supply to blow air into the case instead of out for better air flow, less overlap between the motherboard and drive bays, and integrated I/O Port connectors soldered directly onto the motherboard. The ATX form factor was an overall better design and made it easier to upgrade components (memory, processor, graphic card etc).
The micro-ATX format is an upgrade to ATX, which has the same primary advantages in a smaller format (244x244 mm), with a lower cost.
Micro-ATX includes an AGP connector and 3 PCI connectors. This was done by reducing the number of I/O slots supported on the board. The micro-ATX form factor also provided more I/O space at the rear and reduced emissions from using integrated I/O connectors.
Flex-ATX is an expansion of micro-ATX which offers manufacturers greater flexibility when designing their computers. It includes an AGP connector and 2 PCI connectors.
The mini-ATX is a compact alternative to the format micro-ATX (284x208 mm), and includes an AGP connector and 4 PCI connectors instead of 3 that come with micro-ATX. It is mainly intended for mini-PCs (bare bone computers).
White ATX is the most well-known and used form factor, there is also a non-standard proprietary form factor which falls under the name of LPX, and Mini-LPX. The LPX form factor is found in low-profile cases (desktop model as opposed to a tower or mini-tower) with a riser card arrangement for expansion cards where expansion boards run parallel to the motherboard. While this allows for smaller cases it also limits the number of expansion slots available.
Most LPX motherboards have sound and video integrated onto the motherboard. While this can make for a low-cost and space saving product they are generally difficult to repair due to a lack of space and overall non-standardization. The LPX form factor is not suited to upgrading and offers poor cooling.
Boards based on the NLX form factor hit the market in the late 1990's. This "updated LPX" form factor offered support for larger memory modules, tower cases, AGP video support and reduced cable length. In addition, motherboards are easier to remove. The NLX form factor, unlike LPX is an actual standard which means there is more component options for upgrading and repair.
Many systems that were formerly designed to fit the LPX form factor are moving over to NLX. The NLX form factor is well-suited to mass-market retail PCs.
The BTX, or Balanced Technology Extended form factor, unlike its predecessors is not an evolution of a previous form factor but a total break away from the popular and dominating ATX form factor.
BTX was developed to take advantage of technologies such as Serial ATA, USB 2.0, and PCI Express. Changes to the layout with the BTX form factor include better component placement for back panel I/O controllers and it is smaller than micro-ATX systems. The BTX form factor provides the industry push to tower size systems with an increased number of system slots.
In the BTX form factor the memory slots and expansion slots have switched places, allowing the main components (processor, chipset, and graphics controller) to use the same airflow which reduces the number of fans needed in the system; thereby reducing noise. To assist in noise reduction BTX system level acoustics have been improved by a reduced air turbulence within the in-line airflow system.
The new BTX form factor design is incompatible with ATX, with the exception of being able to use an ATX power supply with BTX boards.
Today, industry tends to accept the ATX form factor as the standard, however some legacy AT systems are still in use.
Since the BTX form factor design is incompatible with ATX, only time will tell if it will overtake ATX as the industry standard form factor.
TIP - If you think your existing motherboard is starting to exhibit a few symptoms that point to failure, check out our motherboard problems page.
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