Micro-ATX

Micro-ATX

Micro ATX followed the ATX form factor and offered the same benefits but improved the overall system design costs through a reduction in the physical size of the motherboard. This was done by reducing the number of I/O slots supported on the board. The micro ATX form factor also provided more I/O space at the rear and reduced emissions from using integrated I/O connectors.

AT & Baby AT (Mother board form facror continued)

AT & Baby AT

Prior to 1997, IBM computers used large motherboards. After that, however, the size of the motherboard was reduced and boards using the AT (Advanced Technology) form factor was released. The AT form factor is found in older computers (386 class or earlier). Some of the problems with this form factor mainly arose from the physical size of the board, which is 12" wide, often causing the board to overlap with space required for the drive bays.
Following the AT form factor, the Baby AT form factor was introduced. With the Baby AT form factor the width of the motherboard was decreased from 12" to 8.5", limiting problems associated with overlapping on the drive bays' turf. Baby AT became popular and was designed for peripheral devices — such as the keyboard, mouse, and video — to be contained on circuit boards that were connected by way of expansion slots on the motherboard.

Motherboard From factor

 Motherboard From factor

The form factor of a motherboard determines the specifications for its general shape and size. It also specifies what type of case and power supply will be supported, the placement of mounting holes, and the physical layout and organization of the board.  Form factor is especially important if you build your own computer systems and need to ensure that you purchase the correct case and components.