Difference Between ATX and Micro ATX

ATX vs Micro ATX

ATX and Micro ATX are form factors of desktop computers. They define the specific nature of the dimension, power requirements and supply, peripheral connector/add-ons, and connector types of the computer system. It primarily concerns the configuration of the motherboard, the power supply unit, and the chassis of the computer system.


ATX is a specification standard of motherboards created by the Intel corporation in 1995 as an advancement from the AT standard. ATX stands for Advanced Technology eXtended. It was the first major change made to the hardware configuration of desktop type computers.

The specification defines the mechanical dimensions, mounting points, Input/ Output panel power and connector interfaces between the motherboard, power supply, and the chassis. With the new specification, interchangeability was introduced in many components of the hardware, in desktop computers.

A full-size ATX board measures 12 inches × 9.6 inches (305 mm × 244 mm). ATX standard introduced the capability to use a separate section of the system for add-ons and extensions for the motherboard, and it is often called the Input/ output panel, which is the panel at the back of the chassis and used to connect devices. The configuration of the I/O panel is set by the manufacturer, but the standard allows ease of access which was not present in the earlier AT configuration.

ATX also introduced PS2 mini-DIN connectors for connecting keyboards and mouse to the motherboards. 25 pin parallel port and RS- 232 serial port were the predominant form of peripheral connectors in the early ATX motherboards. Later, the Universal Serial Bus (USB) connectors have replaced the above connectors. Also Ethernet, FireWire, eSATA, audio ports (both analog and S/PDIF), video (analog D-sub, DVI, HDMI) are installed in the newer versions of the ATX motherboards.

Some crucial changes were made to the ATX power supply too. ATX uses a power supply with three main output voltages at +3.3 V, +5 V, and +12 V. Low-power −12 V and a 5 V standby voltage are also used. The power is connected to the motherboard using a 20 pin connector, which can only be connected in a singular way. This removes the potential of connecting the power supply incorrectly and causing irrecoverable damage to the system, which was a shortcoming of the previous versions. It also gives a +3.3V supply directly and removes the requirement that 3.3V be derived from the 5V supply.

Also, ATX Power supply uses a power switch connected to the power button on the computer case and modification allow the computer to be turned off through the operating system.

Micro ATX

Micro ATX is a standard introduced in 1997 based on the ATX specification. It is also referred to as uATX, mATX, or µATX. The primary difference of the standard comes from the dimensions of the computer system. The maximum size of a micro ATX motherboard is 244 mm × 244 mm.

The micro ATX can be considered as a derivative of the ATX standard. The mounting points are the same; hence allows micro ATX motherboards to be compatible with the chassis of a standard ATX system board. The main I/O panel and the power connectors are the same, allowing peripherals and devices to be interchangeable. TA standard ATX PSU can be used in a microATX system without any problem. They also use the same configuration of chipset, but the size defined in the standard limits the number of expansion slots available.

ATX vs Micro ATX

• ATX is a hardware (motherboard) specification of desktop computers introduced by the Intel Corporation in 1995 as advancement from the existing AT specification.

• MicroATX is a hardware specification introduced based on the ATX specification standard; therefore, it is compatible with the peripherals and add-on devices used for ATX computers. The power supply, I/O panel, and connectors are the same.

• MicroATX is smaller than the standard ATX configuration. It has less expansion slots and fan headers than a standard ATX.

• Chassis of a micro ATX is smaller, but microATX motherboard can be installed in a standard ATX board too.