ATX is an acronym stands for Advanced Technology Extended. It is a motherboard configuration specification developed by Intel in 1997 to improve the previous standards like the AT design. It totally changed the desktop computer enclosure, motherboard and power supply design in many years and improved the standardization and interchangeability of parts.
ATX defines the key mechanical dimensions, mounting point, I/O panel, power and connector interfaces between a computer case, a motherboard and a power supply. It is the most common motherboard design. It has some other standards for smaller boards (i.e. microATX, FlexATX, mini-ITX and extended ATX) which usually keep the basic rear layout but reduce the size of the board and the number of expansion slots.
It is more economical than previous AT form factor.
The size dimensions of a full-size ATX board are 12 × 9.6 inches (305 × 244 mm). It facilitates many ATX chassis to also accept microATX boards. The official size specification of ATX was released by Intel in 1995 and have been revised many times after that.
The latest ATX motherboard specification is version 2.2. The latest ATX12V power supply unit specification is 2.31, released in February 2008.