PC Form Factors Computers come in different form factors. ATX is the most common. AT used to be the standard but is now obsolete. NLX and LPX are two others. These forms describe the shape and size of the motherboards, as well as the layout of the components on the board. The form factor will also determine the type of case you must buy, as the case is laid out differently and uses a different type of power supply. AT Form Factor Within the AT form, we have regular AT and Baby AT. They basically differ in size. An AT board is about 12" wide which means it can't fit in many of today's cases. AT boards generally are the older boards, 386 or earlier. Working inside the case was a lot more trouble with these because the size of the motherboard overlapped drive bays and such. Baby AT is the form used by many 486 and Pentium boards.. Many Socket 7 motherboards and a few Pentium II boards used this form factor. A Baby AT board is roughly 8.5" wide and 13" long. The size 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 the case. AT form boards share common traits. They all have serial and parallel ports attached to the case in an expansion slot and connected to the board through cables. 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. There are some annoyances with the AT design. One is due to the layout. Since all ports are attached to the case and then connected to the motherboard via a cable, the board must have connectors for all of these: COM 1, COM 2, printer port, USB, PS/2 mouse, etc. Often these connectors are directly next to the IDE channel connectors and floppy drive connector. This leads to a severe cramping problem and makes working inside the computer more difficult. Secondly, the AT design is not conducive to efficient cooling of the system. Air is not blown over the areas that need it, namely the CPU. Also, the air flow draws in dust. Over time, the AT power supply will get dusty and the inside of the system will be coated with a layer of dust. For this reason, it is recommended you regularly remove the case and blow off the interior of the case. 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. NLX Form Factor NLX is intended for low-profile PC's. NLX systems uses a riser board, similar to the LPX form. The riser boards sits vertically in the case and is connected directly to the power supply. Each of the expansion cards connect directly to this riser board, as well as the HDD and FDD connectors that usually reside on the motherboard itself. So, basically, the riser card is the hub of the NLX system, with everything connecting to it. Even the NLX motherboard can simply be removed from its slot on the riser card and replaced. An NLX motherboard looks different than that of AT of ATX. The first thing you'll notice is that it has no expansion card slots nor does it have any drive connectors. As said before, all this has been moved to the riser card. Also, you will notice a 340-pin connector on the side of the motherboard. This is what interfaces with the riser card. Like ATX, the I/O connectors are on a panel on the rear of the board, and like ATX, this part of the board sticks out of the case so you can connect your USB, parallel and serial devices to the NLX system. The power supply looks similar to that of an ATX machine, and connect to the motherboard via a 20-pin connector. It has a single exhaust fan which happens to be also placed near where the CPU is placed on the motherboard, so that the power fan can help cool the NLX system. LPX Form Factor LPX is like an older AT-version of the NLX form factor. LPX motherboards have the same, if not smaller, dimensions as a baby-AT motherboard. They also share the same AT-style power connectors: two 6-pin connectors usually labeled P8 and P9. Like NLX, it uses a riser card as the hub of the system. The external I/O ports on an LPX system follow the same format usually: (from left to right) VGA, parallel port, 2 serial ports, PS/2 mouse, PS/2 keyboard. Some newer versions alter this layout to accomdate USB and possibly LAN connections. LPX, back in its day, was taken on by several manufacturers, and it was used pretty much up until the Pentium II days. But, with the lack of standardization, it did not go beyond that. LPX riser cards had to meet certain electrical requirements, but beyond that, the arrangements of the various connectors varied from manufacturer to manufacturer. This led to difficulty in upgrading because you could not just swap out riser cards. Thus, it had a limited life. .