Micro ATX (or ?ATX) is a form factor motherboard available in different sizes from 9.6' x 9.6'to 6.75' x 6.75'. The motherboard supports Intel, VIA, and AMD chipsets or CPUs. The motherboard was released in 1997 and it was designed as a replacement for ATX form factor motherboards. Some of the advantages of this motherboard over the ATX form factor motherboards it replaced include the smaller and more compact size, the integrated devices which means fewer expansion slots, lower chassis cost, lower consumption of power, and several others. ATX form factor motherboards were developed in 1995 by Intel. microATX is backward-compatible with the original ATX. The mounting points are subsets of those used by ATX motherboards and the I/O panels are also identical. This means microATX motherboards can fit in the cases of ATX motherboards. ATX motherboards and microATX motherboards also share power connectors. The two boards also share chipsets which are southbridges or northbridges. However, cases for microATX are generally smaller. The standard ATX motherboard size is 25% longer than a microATX motherboard at 12' wide x 9.6'deep.
Modern ATX form factor motherboards come with more than 5 PCI/ PCI-Express expansion slots while microATX form factor motherboards only come with 4 as the maximum. This is the reason why microATX motherboards come with integrated peripherals such as integrated graphics cards. An example of this is Asus A8N-VM CSM motherboard which comes with an onboard GeForce 6 graphics card, AC'97 audio card, and a gigabit Ethernet adapter. The power supply has three main outputs and these are +3.3 V, +5 V and +12 V. You could also get supplies with 5 VSB (for standby) and ?12 V (for low power). microATX cases support 6 SATA devices and 4legacy IDE drives only. If you so wish, you could maximize the capability of these motherboards by setting them on ATX cases. Note that some microATX cases that use power supplies that do not have standard dimensions will require LP PCI cards.
The careful design of microATX motherboards is done to give cost savings resulting from reduced output power supply, reduced costs of chassis, and minimum redesign of older ATX-compliant chassis. Other benefits of microATX motherboards over traditional ATX motherboards are space saving, meaning the case can easily fit in a small work station, more I/O spaces at the rear, and reduced emissions because of integrated I/O connectors. These motherboards have 'must-have' functions and you therefore need to know what these are when going computer shopping. Other form factor motherboards that are competing with Micro ATX include Nano-ITX 120 ? 120, ESMexpress125 ? 95, COM Express 125 ? 95, Mini-ITX 170 ? 170, BTX 325 ? 266, Baby-AT 330 ? 216, ETX/XTX 114 ? 95, PC/104 (-Plus) 96 ? 90, Pico-ITX 100 ? 72, FlexATX 229 ? 191, EBX 203 ? 146, ESMini 95 ? 55, LPX 330 ? 229, microBTX 264 ? 267, DTX 244 ? 203, Mini-DTX 203 ? 170, and EPIC (Express) 165 ? 115.
You could get specifications from the latest version and revisions of microATX Motherboard Interface Specification which indicate key changes such as the recent change of the pins in the Main Power Connector which changed from 20 for PCI interface to 24 ( 2 x12) to support PCI-Express interface.
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This article touched the basics of the topic. I have 2 more resources related to the above. They are micro atx and micro atx . Do consider reading them.
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