ATX

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. Almost all Pentium II and later boards are ATX, although there were some AT Pentium II boards available. Pentium boards were still primarily AT, although many manufacturers have released ATX versions. ATX is now THE form factor, and it would be a bit difficult to buy anything else.

The ATX design is a vast improvement over AT. It fixes the annoyances of the AT form. Since the AT form was so old, as new demands were placed on it from new technology, little problems began to show up. These problems are taken into account with ATX.

Some features are:

• 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 reach around a drive, or even remove the drive, in order to reach certain areas of the motherboard. 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, 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 or heat sink.


• User-Friendly Power Connector: ATX uses one 20-pin connector to attach to the motherboard. The ATX connector is also keyed so that it will only go in the correct way. This is easier than the two separate connectors of the AT form which look almost the same. 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.


• 3.3 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. It must be noted, though, that many processors don’t use this voltage, and therefore must use a voltage regulator anyway.


• A Little Automation: The ATX power supply is capable of being controlled through software and other means. This is because it always has a slight voltage going through it. This gives the computer the ability to turn itself on at specified times and perform some task given to it by the software. Some ATX motherboards have the option of turning the system on by pressing the space bar on your keyboard or being woken up by a command sent down through the LAN. Lastly, the shut down procedure is automated using ATX. When one uses Win95 and chooses “Shut Down”, the computer will perform all shut down tasks, then turn itself off. Not too shabby.

You can see a diagram of an ATX motherboard at: ATX Slot 1 Motherboard.