What is the relationship of type of motherboard and the size of ram

The real relationship to maximum supported RAM is the CPU limits.

Examples:
LGA 1366 Bloomfield = 24GB {6X4GB}
LGA 1155 Sandy Bridge = 32 GB {4X8GB}

Some Server boards are 192GB~256GB+.

4CPUs 64GB/CPU:
13-151-219-TS

 


Look at the motherboard specs.

Workstation motherboards may be able to support as much as 256gb of ram. More common P67 motherboards can support up to 32gb using 4 x 8gb sticks.
Some 1366 motherboards can support up to 48gb, again using 6 8gb sticks.

But... 8gb sticks are not yet available, so the real current limit is half.