::: Whatever the size of user space is, yes, each process gets its own. If you consider all of the processes at once, then yes, the total VAS might be much larger than 8 TB (if that is the limit)... assuming of course that there is RAM+backing store to put it all! But only one process's VAS can be mapped at a time—that is, only one can be addressable at a time. They all use the same user space addresses as each other. So the total virtual address space addressable at any moment (on any one logical processor) is that of one process's user mode address space plus the kernel mode address space. x64's 48-bit canonical addresses limit that total to 256 TB no matter how many processes Windows defines. Prior to 8.1, Windows limited the total to 16 TB, for reasons well described here.