Normal
Standard MicroATX is 244x244mm, which is physically impossible to fit inside the M1 - that's larger than the entire chassis in one dimension (240mm). The absolute maximum size a board can be in the M1's height dimension is 226mm. Coincidentally, there are a small number of in-between size boards - usually with two or three expansion slots, rather than four - that are right around that size. Unfortunately, these tend to be lower end, budget boards, so unless you really need an extra expansion slot, they're not really worth it. You can find an older thread discussing mATX in the M1 here.This board, which someone has fit in the M1, is something of an exception to the low end-only rule.
Standard MicroATX is 244x244mm, which is physically impossible to fit inside the M1 - that's larger than the entire chassis in one dimension (240mm). The absolute maximum size a board can be in the M1's height dimension is 226mm. Coincidentally, there are a small number of in-between size boards - usually with two or three expansion slots, rather than four - that are right around that size. Unfortunately, these tend to be lower end, budget boards, so unless you really need an extra expansion slot, they're not really worth it. You can find an older thread discussing mATX in the M1 here.
This board, which someone has fit in the M1, is something of an exception to the low end-only rule.
