what is the different between form factor ?

Solution
Form factor of mobos refer to their physical sizes.

microATX : 6.75 × 6.75 in (171.45 × 171.45 mm) to 9.6 × 9.6 in (244 × 244 mm)

ATX : 12 × 9.6 in (305 × 244 mm)

E-ATX : 12 × 13 in (305 × 330 mm) [12 × 10.1 in (305 × 257 mm), 12 × 10.4 in (305 × 264 mm), 12 × 10.5 in (305 × 267 mm) and 12 × 10.7 in (305 × 272 mm)]

Server System Infrastructure (SSI) Forum's Compact Electronics Bay (CEB) form factor measures 12 × 10.5 in (305 × 267 mm)

XL-ATX : 13.5 × 10.3 in (343 × 262 mm) [12.8 × 9.6 in (325 × 244 mm), 12.8 × 10.0 in (324 × 253 mm), 13.6 × 10.4 in (345 × 264 mm)]

HPTX : 13.6 × 15 in (345 × 381 mm)
Form factor of mobos refer to their physical sizes.

microATX : 6.75 × 6.75 in (171.45 × 171.45 mm) to 9.6 × 9.6 in (244 × 244 mm)

ATX : 12 × 9.6 in (305 × 244 mm)

E-ATX : 12 × 13 in (305 × 330 mm) [12 × 10.1 in (305 × 257 mm), 12 × 10.4 in (305 × 264 mm), 12 × 10.5 in (305 × 267 mm) and 12 × 10.7 in (305 × 272 mm)]

Server System Infrastructure (SSI) Forum's Compact Electronics Bay (CEB) form factor measures 12 × 10.5 in (305 × 267 mm)

XL-ATX : 13.5 × 10.3 in (343 × 262 mm) [12.8 × 9.6 in (325 × 244 mm), 12.8 × 10.0 in (324 × 253 mm), 13.6 × 10.4 in (345 × 264 mm)]

HPTX : 13.6 × 15 in (345 × 381 mm)
 
Solution