The two motherboards share a lot in common, but the main difference comes in when taking into account their RAM slots. For B450, you will have up to 4 slots. You can support up to 64GB of RAM on the B450. For the case of B450M, you are limited to two slots that can support a maximum of 32GB of RAM. If you are looking for more RAM capacity, you will have to opt for B450 because it is built to support more RAM.