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Replacing your motherboard: Which form factor is best?

If your current motherboard can't take your system any further, read this Daily Feature by Ken Dwight, who explains all about current form factors and upgrades.


If you have already increased RAM as much as is practical and your present motherboard contains a processor at or near the maximum speed supported by the board, it’s time to consider replacing your motherboard.

Form factor facts
If you’re considering this step, first you need to know the form factor of the motherboard you have installed. Form factor refers to the size and shape of the motherboard, the types of connectors on the board, their layout, and how the board fits into the computer case.

Avoid proprietary designs
Some computer manufacturers (Compaq, for example) design proprietary motherboards, which usually are not cost-effective to upgrade. Non-standard form factors are more expensive, and supplies are limited. When the production run of a certain model is over, it’s likely you won’t be able to upgrade that computer’s processor any more. In contrast, using a standard form factor always presents a longer upgrade path. Many manufacturers use these standards, resulting in more choices and less cost.

If your system falls into the proprietary category, your best bet for upgrading is to buy a new standard motherboard, along with a compatible case and power supply. You can then transfer components from the proprietary system to the new case.

Grade A forms
There are three important standard form factors: AT, Baby-AT, and ATX. The oldest is the AT, so called because it was designed to fit the IBM PC-AT case. Baby-AT developed from AT and kept the same orientation but was about one-third shorter in length than the full AT boards. Baby-ATs allowed computer manufacturers to make more compact systems. Baby-ATs can fit in AT cases because they share standard attachment points, and AT-style cases are designed with standard windows to accommodate AT-style on-board ports and peripheral cards. Be aware, however, that an AT board probably won’t fit in a Baby-AT case. If you want to upgrade to an ATX board from a Baby-AT, you’ll probably need to replace the case as well, and possibly the power supply.

These days, most standard AMD or Pentium class motherboards come in two form factors: Baby-AT or ATX. Systems built in the past few years more often use the ATX type. While it might be possible to find AT or Baby-AT motherboards with the latest processors and busses, these designs are phasing out.

The older boards included the circuitry for most supported input/output devices, including the primary and secondary IDE controllers, the floppy disk controller, serial, parallel, keyboard, and mouse ports. Recent Baby-AT and ATX boards support USB ports and possibly other interfaces, such as FireWire.

Recognizing AT boards
Regardless of the devices supported by an AT-type board, the board itself typically contains only one connector, for a DIN-style keyboard (See Figure A). All of the other external devices require ribbon cables to connect the pins on the motherboard to brackets mounted on the back of the case.

Figure A
AT and Baby-AT motherboards can be recognized by their lone DIN connector.


Recognizing ATX boards
The ATX form factor hit the streets in 1996. These motherboards improved the Baby-AT design in a number of ways and have become the standard configuration for motherboards in new systems.

The most apparent improvement in ATX boards over the Baby-AT is the addition of a bracket housing all the external connectors. These include serial and parallel ports, keyboard, mouse, USB, and optionally video, network, sound, and modem connections. Having this bracket with the connectors on it eliminates the need for ribbon cables running from the motherboard to individual brackets mounted on the back of the case, as is required with Baby-AT boards.

The next obvious difference between an AT-style motherboard and ATX is the orientation of the board itself. AT and Baby-AT boards are deeper than they are wide; in other words, the board is longer from the front of the case to the back than from one side to the other. ATX boards are wider than they are deep, which is to say they have been rotated 90° with respect to the AT-style boards.

Power connector improvements
An important improvement offered by ATX motherboards is the type of power supply connectors they use. AT-style power supplies use two cables, designated P8 and P9, to apply power to the motherboard. These two connectors fit into a single connector on the motherboard. These AT connectors are not usually adequately keyed, making them easy to attach incorrectly to the board. When that happens, the motherboard can be damaged by the improper flow of current through the board.

ATX power supplies, on the other hand, use a single, keyed connector to mate to the motherboard. This connector can only be attached one way, thus minimizing the likelihood of motherboard damage as a result of improper power supply connection.

Other benefits
There are at least two more benefits of ATX motherboards resulting from the board’s orientation. First, the processor is positioned nearer to the power supply, which results in improved CPU cooling; similarly, the IDE controller connections on the board are closer to the hard drives in the system, which allows for shorter hard drive cables and consequently improved reliability of the drives.

Conclusion
Considering the newer design of ATX boards, increased functionality, and reduced workload as a result of the built-in bracket with connectors already attached, you may want to go ahead and convert. Converting to this form factor now will allow you to have the most reliable and least costly upgrade path for years to come.
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