What's the difference between uATX and micro ATX motherboards?

Question

I'm looking to build a new PC and am trying to decide between using a uATX or micro ATX motherboard form factor. Can someone explain the key differences between uATX and micro ATX? Specifically:

How do uATX and micro ATX differ in terms of physical size and dimensions?
Are there differences in the number of expansion slots and RAM slots between the two?
Is one generally better for certain use cases like gaming PCs or HTPCs?
Are there compatibility considerations with uATX vs micro ATX in terms of fitting in different PC cases?

I'd appreciate any insights from those with experience building PCs using these motherboard form factors. Links to any good comparison articles would also be very helpful.

Thanks in advance!

Flake_Tom · Answer

Here is a comparison of the key differences between uATX (ultra ATX) and micro ATX motherboard form factors:

Physical Size and Dimensions:

Micro ATX: 9.6" x 9.6" (244mm x 244mm)
uATX: Typically 9.6" x 7.5" (244mm x 191mm)

So uATX boards are shorter in height than micro ATX by about 2 inches (53mm). Both have the same width.

Expansion Slots:

Micro ATX: Typically has 4 expansion slots
uATX: Usually limited to 2-3 expansion slots due to the smaller size

The reduced height of uATX means fewer PCIe slots for graphics cards, expansion cards, etc.

RAM Slots:

Micro ATX and uATX both commonly have 2 or 4 RAM slots
The number of RAM slots is more dependent on the specific motherboard model than the form factor

Use Cases:

Micro ATX is very popular for mainstream gaming PCs and general purpose desktops
uATX is often used for compact PCs, HTPCs, and small form factor gaming builds where a very small footprint is needed
uATX's limited expansion slots can be restrictive for high-end gaming PCs with multiple graphics cards

Case Compatibility:

Micro ATX will fit in any case designed for standard ATX or micro ATX motherboards
uATX will fit in any micro ATX case as well as some specially designed uATX mini tower and HTPC cases
Many mini ITX cases are also compatible with uATX motherboards

So in summary, the main differences are:

uATX boards are shorter in height by about 2"/53mm
uATX has fewer expansion slots (2-3 vs 4)
micro ATX is more versatile, uATX is for more compact builds

Some helpful comparison articles:

Let me know if you have any other questions! Happy to clarify or provide additional details.