PC motherboards typically follow a common standardized form factor. The form factor describes the physical dimensions, placement of components, connectors, and so on. Computer cases are generally designed for one motherboard form factor.

However, notebook systems and Apple Macintosh PCs don't necessarily follow the same form factor conventions.

Some modern motherboard form factors include:

**ATX (Advanced Technology Extended)**
  * Dimensions: 305mm x 244mm (Approx. 12 x 9 5/8 inches)
  * Very typical PC motherboard
  * Designed back when airflow wasn't a principle concern
  * Expansion and memory slots are positioned perpendicularly.
  * Uses a 20 or 24 pin power connector
  * Software power on/off switch.
  * Has an I/O port plate
  * Popular in full-size PCs

**microATX (Micro Advanced Technology Extended)**
  * Dimensions: 171mm × 171mm (Approx. 6 3/4 x 6 3/4 inches)
  * Slimline version of ATX for small desktops
  * Shares characteristics of ATX
  * Compatible with ATX cases
  * Fewer expansion slots
  * Popular form-factor

**NLX (New Low-Profile Extended)**
  * Dimensions: 254mm × 228mm (Approx. 10 x 9 inches)
  * Smaller size than ATX
  * Mandatory AGP bus support
  * Has a large riser board connector
  * Riser card provides expansion slots
  * Compatible with ATX power supplies but not cases.

**BTX (Balanced Technology Standard)**
  * Dimensions: 325mm × 266mm (Approx. 12 13/16 x 10 1/2 inches)
  * Large PC motherboard form-factor
  * Designed to support new technology (SATA, PCIe)
  * Improved overall airflow characteristics
  * Expansion and memory slots are positioned in parallel
  * CPU ZIF socket or slot is positioned at a 45 degree angle
  * Incompatible with ATX power supply and cases
  * No longer in production

**MicroBTX (Micro Balanced Technology Extended)**
  * Dimensions: 264mm x 266mm (Approx. 10 3/8 x 10 1/2 inches)
  * Smaller PC motherboard good for low-profile desktops
  * Shares characteristics of BTX
  * Still popular today

**PicoBTX (Pico Balanced Technology Extended)**
  * Dimensions: 203mm x 266mm (Approx. 8 x 10 1/2 inches)
  * Very small motherboard for perhaps embedded devices
  * Shares characteristics of BTX
  * One expansion slot
  * Still popular today