Also worth noting that the entire stack isn't allocated at once so 1 million threads would be using 2TB/68GB of virtual address space, not 2TB/68GB of physical memory.
That is indeed a very important fact to keep in mind! Thread stack sizes have been a problem with 32 bit systems where you quickly run out of virtual memory because the adress space is not large enough. With 64 bit that is not a problem anymore.
