Mother Board Types

A motherboard form factor just describes the dimensions or size of the motherboard and what the layout of the motherboard components are. It is important to understand the different motherboard form factors, because you cannot take any motherboard and place it in a computer case. You must put an ATX board in an ATX case.

Full AT

The first type of motherboard that we want to talk about is the full AT motherboard. The full AT motherboard is 12 inches wide and 11 inches long. The full AT suffered from a problem with accessing some of the items on the motherboard because the drive bays hung over the motherboard. This situation made installation and troubleshooting of the components on the motherboard very difficult.

Another problem with the layout of the full AT board is that the expansion cards, once inserted into the systems, would cover the processor. This situation led to cooling problems due to the fact that ventilation was insufficient to keep the chip from overheating.

Baby AT

The baby AT system board form factor has been one of the most popular motherboard types until recent years. The baby AT board is 8.5 inches wide and 10 inches long. This motherboard can be easily recognized because it usually has a DIN keyboard connector in the top-right corner of the board.

The baby AT board was about two-thirds the size of the full AT board and incorporated a socket 7 ZIF slot for classic Pentium processors. The baby AT board usually had a mixture of ISA/EISA and PCI slots located on the system board and included a plug and play BIOS.

Take a minute to consider some of the key components on the baby AT motherboard The socket 7 ZIF slot is usually situated at the bottom of the motherboard where the processor is to be installed. Also notice the SIMM and DIMM sockets on the right side of the motherboard, which are used to house RAM memory. To the left of the SIMM and DIMM slots, are the primary and secondary EIDE controllers for connecting the hard drives to the board. To the left of the EIDE controllers, notice the types of expansion slots that are used: There are four PCI slots and three EISA slots. Above the PCI slots, there is a silver circle, which is the CMOS battery.


In 1995, Intel wanted a system board that would be used to support the Pentium II processor and the new AGP slot, so the ATX form factor was built. The ATX board is 7.5 inches wide and 12 inches long and has all the IO ports integrated directly into the board, including USB ports. The ATX board introduced a 100 MHz system bus, whereas older Pentium boards ran at 60/66 MHz and had one AGP slot for video cards. The ATX board also had soft power support, which meant that the system could be shut down by the operating system. The ATX form factor rotated the baby AT components by 90 degrees so that any cards inserted into the bus architectures would not cover the processor and prevent proper cooling.

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