Maximum RAM on X99 boards

[fregimus]

Some X99 motherboards indicate maximum RAM supported as 64MB, while other support 128MB. They all have 8 DDR4 slots. Why is the difference? Is not this a chipset limitation?

 

[Phillip Corcoran]

Chipset is irrelevant, it's a limitation of the memory controller.

 

[fregimus]

Chipset is irrelevant, it's a limitation of the memory controller.

Thanks, but now I am even more confused. The memory controller is integrated into the CPU, and all X99 boards support the same set of 3 higher-end Haswell i7's that come in the LGA 2011-v3 package. So what exactly is the limitation you are talking about, and how come this limitation is apparent on some motherboards while others manage to circumvent it? Why does the very same CPU's on-die MCU support different max RAM amount on different boards?