| A motherboard form factor used in some desktop model PCs. The distinguishing characteristic of LPX is that expansion boards are inserted into a riser that contains several slots. So the expansion boards are parallel to the motherboard rather than perpendicular to it as in other common form factors, such as AT and ATX. The LPX design allows for smaller cases, but the number of expansion boards is usually limited to two or three. Within the AT form, there is regular AT and Baby AT. They basically differ in size. An AT board is about 12" wide, meaning it can't fit in many of today's cases. AT boards are generally older, usually used with a 386 or earlier. Baby AT boards are the mainstream of today. Of course this is changing with the presence of ATX, but Baby AT is still the most popular form factor, simply because of the amount of AT hardware being used these days. A Baby AT board is 8.5" wide and 13" long. The length varies a little from board to board. This reduced size makes it easier to work inside the case simply because there is more room. There are three rows of mounting holes to hold the board in place. | They also have a single keyboard connector soldered onto the board at the back of the board. The processor is still at the front of the board and can sometimes get in the way of expansion cards. The SIMM slots are in different places, although they are almost always at the top of the board. AT form boards share common traits. They almost all have serial and parallel ports attached to the case and connected to the board through pin headers. In 1995, Intel released the ATX form factor. It was slow to catch on due to the long-time acceptance of the AT board, but slowly it gained popularity. All Pentium Pro boards are ATX. Pentium boards are still primarily AT, although many manufacturers release ATX versions. |
| The ATX design is a vast improvement over AT. It fixes the annoyances of the AT form. Since the AT form was so old, new demands were placed on it from new technology, and problems began to show up. These problems are taken into account with ATX. -
Integrated I/O Connectors -
While the AT uses headers on the board that are attached to the actual ports on the back of the case, the ATX board has the actual ports built right onto the board. This makes installation easier and enhances reliability. Integrated PS/2 Mouse Connector -
Reduced Overlap Between Board and Drives -
The ATX board looks like it is rotated 90 degrees so that it does not overlap the drive bays in the front. This way, one can reach the entire board instead of having to work around a drive, or even remove the drive. This also reduces heat. Reduced Processor Interference with Cards -
The processor is moved from the front of the board near the slots to the back and top of the board, near the power supply. This means that a user can install full-length expansion cards in the slot without having to worry about hitting the CPU. User-Friendly Power Connector -
ATX uses one 20-pin connector to attach to the motherboard. This is easier than the two connectors that look almost the same in the AT design. It also gets rid of the problem of "frying" the board due to misplacement of the connectors on the motherboard. Better Cooling Conditions -
The ATX power supply blows air into the case instead of out. This means that air blows out all the holes in the case and thus keeps dust out. Also, due to the processor's placement near the power supply, the supply's own fan blows air over the heat sink, removing the need to a CPU fan. -
Volt Power. The ATX motherboard is designed to accept 3.3 volt power directly from the power supply. Since almost all modern processors operate at 3.3 volts, this removes the need for a voltage regulator on the motherboard to reduce the voltage from 5V to 3.3V. |
