A single 128GB mainboard is $2000, so four of them is $8000. Not the same as a machine with 512GB of unified memory.
For the M4 Mac Studio, it costs $4800 to upgrade from 32GB to 128GB. I believe everything else “base model” is $2000, for a total of $6800, but this is also a full working computer and not just a mainboard.
A single 128GB mainboard is $2000, so four of them is $8000. Not the same as a machine with 512GB of unified memory.
For the M4 Mac Studio, it costs $4800 to upgrade from 32GB to 128GB. I believe everything else “base model” is $2000, for a total of $6800, but this is also a full working computer and not just a mainboard.