You're barking up the wrong tree. Nobody's manufacturing power-of-ten sized DRAM chips for NVIDIA; the amount of memory physically present has to be 128GiB. If `free` isn't reporting that much usable capacity, you need to dig into the kernel logs to see how much is being reserved by the firmware and kernel and drivers. (If there was more memory missing, it could plausibly be due to in-band ECC, but that doesn't seem to be an option for DGX Spark.)