Technical PC Form Factors

PC Form Factors

Personal Computers come in different form factors of which AT and ATX are the most popular. NLX, LPX, ATX and AT describe the shape and size of the motherboards, as well as the layout of the components on the board. The form factor also determines the case as it is laid out differently and uses a different type of power supply.

AT Form Factor

Within the AT form there is regular AT and Baby AT. They are basically different in size. An AT board is about 30 cm wide (12 inches) and will not fit in many of today's cases. AT boards are generally found in older computers. A Baby AT is the form used on most boards and cases today. Baby AT is approximately 22 cm wide (8.5 inches), but the size varies from board to board. Reducing the size made it easier to work inside the case. AT boards all have serial and parallel ports attached to the case in an expansion slot and connected to the board by ribbon cables, a five pin DIN keyboard connector soldered on the board, the processor is at the front of the board and the SIMM slots are usually almost always at the top.

ATX is much more advanced. The AT design is annoying and leads to severe cramping and sometimes overheating. Air is not blown over areas that need it.

ATX Form Factor

The ATX form features integrated I/O connectors. The ports are built on to the board, making installation easier and more reliable. Integrated PS/2 (small mini 6 pin DIN plug) mouse connector and a 20 pin power connector to the motherboard which is keyed so that it will only go in one way and one connector instead of the two separate connectors of the AT form. The ATX power supply blows air in to the case instead of out, so the air blows out all the holes and keeps them fairly dust free. The power Supply is also capable of delivering 3.3 volts which is required by the current processor designs and removes the need for a voltage regulator on the motherboard. The ATX power supply is also controllable through software because it always has power going through it. The computer has the ability to turn itself on at specified times and perform tasks as well as an automated shutdown when using the Windows 9x or Linux 7 operating systems and choosing 'Shut Down' the computer.

NLX Form Factor

NLX is a newer form factor intended for low-profile personal computers. NLX uses a riser board that sits vertically in the case and is connected directly to the power supply. Each expansion card connects directly to this riser. An NLX motherboard does not have any expansion slots or drive connectors. There is a 340 pin connector on the side of the board that interfaces with the riser card. The I/O connectors are on the rear edge of the board allowing easy connection of USB, parallel and serial devices.

LPX Form Factor

LPX boards are often smaller than Baby AT motherboards and share the same power connectors. LPX also uses a riser card as the hub of the system. The external I/O ports are also located on the rear of the board and stick out of the case. The arrangement of various connectors on the riser changes from each manufacturer and leads to difficulty upgrading if you can not just swap out riser cards.

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