Answer:
It is important for your case to share a compatible form factor because different cases have different compatibilities. For example if you have a Micro-ATX case, a full ATX motherboard would be too large to fit into that case.
You might want to use a slimline form factor if you have limited space.
With a full ATX you will be able to add more as well as larger components, where as if you get a Micro-ATX, you would be limited.
The two OS are Linux and Windows.
Normally you can eye ball it by determining the size and shape of the case.
Step-by-step explanation: