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The AT & Baby AT Form Factors
Form factor design has had an interesting history. IBM designed the Advanced Technology (AT) form factor in 1984. Its dimensions were 12 × 11–13 in or (305 × 279–330 mm). The IBM PC was introduced in 1981, but the vaunted AT model was released three years later.
The rise of the motherboard's defacto importance continued as more chips and circuits were added to it, correspondingly making the motherboard area smaller. Problems with the AT form factor were due principally with the physical size of the board. At 12" wide, it would cause the board to overlap with space required for the drive bays. The Baby AT form factor was released in 1985 by IBM, with dimensions 8.5 × 10–13 in (216 × 254–330 mm). Clearly, the size reduction made the overlap problem disappear.
The following image breaks down the different components of a motherboard.
While the size of the Baby AT solved some problems, it also created others. The Baby AT form factor did not provide the space to use a combination of processor, fan and heat sink. To solve these space issues, a new form factor design took place, namely the ATX.
The Baby AT and AT boards have similar dimensions, but the ATX board has a 90 degrees rotation within the case to allow for easier access to components.
Other information about form factors is available at What is a Motherboard Form Factor?
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The ATX Form Factor
By 1995 the motherboard had become laden with new chips of various sizes. Intel released the ATX. Its dimensions were 9.6 x 12 in (244 x 305 mm).
The ATX form factor introduced many chances to the computer. First was the size. Expansion slots used separate riser cards that plugged into the motherboard. So the overall size of the computer and its case size was slightly reduced.
The ATX form factor also brought about changes to the motherboard, and to the case and power supply. The new form factor overcame some of the earlier problems with air flow, which could cause heat damage to the motherboard.
There was a power supply improvement with a single 20-pin connector; the power supply was able to blow air into the case instead of out, resulting in better heat dissipation and air flow. Furthermore, there was less overlap between the motherboard and the drive bays. The integrated I/O Port connectors were directly soldered onto the motherboard. Upgrading the motherboard was now possible.
This form factor is considered the defacto industry standard for motherboard design. You can also read about
How Motherboard Technology Has Evolved for additional details.
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The MicroATX Form Factor
Following the success of the ATX, which showed that by separating features or placing chips and slots in different locations, additional space and energy savings could be accomplished, new form factors were developed.
The MicroATX was a smaller version of the ATX form factor (actually about 25% shorter). It was released in 1996. The size is 9.6 × 9.6 inches (244 × 244 mm). It was compatible with most ATX cases but came with fewer slots than the standard ATX. It also came with a smaller power supply unit. The reduction in motherboard size and cost included limiting the number of I/O slots supported on the board. It also provided more I/O space at the rear. It reduced heat from using integrated I/O connectors. Its size made it popular for desktop and small form factor computers as of 2007.
But the small size did not end there. Here is a comparison of the various ATX form factors. Their dimensions identify their processing capabilities, and the intended commercial market. Several different form factors were introduced. At one end is the business-server computer and at the other end is the laptop systems. Here are the dimensions of these different form factors:
You can also read about the Small Form Factor PC
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The LPX Form Factor
While the ATX is the standard form factor, the LPX (Low Profile Extended) is a non-standard form factor. This is a smaller motherboard with dimensions in the 9 × 11–13 inch range (229 × 279–330 mm). It is typically found in desktop models, as opposed to the mini-tower format. Usually they have sound and video integrated into the motherboard. This saves costs but it is more difficult to maintain as it is a non-standard form.
This form factor has size reduction as the main goal. By reducing the power supply height, it had the result of facilitating the form factor design of a much smaller and in consequence consumer-friendly PC. The connectors for the LPX are the same as those of the Baby AT and AT.
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The NLX Form Factor
The NLX (New Low Profile Extended) design, introduced by Intel in 1997, improves on the LPX design. The emphasis is on ease of maintenance. The dimensions are between 8–9 X 10–13.6 inch (203–229 × 254–345 mm). This size fits well for low-profile desktop cases.
With this design, the expansion slots, peripheral connectors and power cables are on an edge-mounted riser card. Using this configuration, the simple removal of the connections from the main motherboard is possible. The motherboard uses a full-width I/O shield that allows different combinations to take place in the rear-panel I/O.
An AGP card can be used, but the slot must be on the motherboard. This is a drawback because it is harder to maintain troubleshooting or update operations on such a card.
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The BTX (Balanced Technology Extended) is a new standard proposed by Intel as a successor to the ATX form factor.Its dimensions are 12.8 × 10.5 inch (325 × 267 mm) max. It was proposed in 2004, and according to Intel the form factor has better cooling features and is markedly different from the ATX. The BTX Boards have a different structure, flipped over when compared to ATX Boards, making a BTX or MicroBTX Board work only with a BTX case, while an ATX form factor board will only fit in an ATX case.
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As of 2007, motherboards used on desktop computers, even those found on Macintosh and Sun computers, use standard form factors. The de-facto form factor for PC desktops at this time is the ATX. A case's motherboard and form factor configuration must all work and match together. However, some smaller form factors from the same motherboard family will fit in larger cases. For example, a microATX form factor will usually fit in an ATX case. The microATX form factor is typically several inches smaller in dimension than the case.
The latest innovation is the BTX form factor, which entered the market in 2004. Intel intended to make this the next generation form factor with additional cooling features, and not just a variant of the ATX, and so it requires a specialized case.
Understanding other form factors is available at Understanding the Motherboard Form Factor CEB.
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Source: PC Computer Notes
Baby AT Form Factor Image credit Wikipedia Commons in the public domain
ATX Form Factor, Image credit Wikipedia Commons in the public domain
MicroATX Form Factor, Image credit Wikipedia Commons in the public domain
BTX Form Factor, Image credit Wikipedia Commons in the public domain