I have a question regarding multilevel page tables. As far as I know, in most 64 bit systems only 48 bits are used in page tables which would allow for 256TB of virtual memory to be addressed.For personal computers, I don't understand how they would ever be able to support that amount of memory being virtualized. If the processes currently running on your computer think they have a total of 256TB available, if they do end up using all that memory, the contents would eventually need to be flushed back to disk. This is not possible since your disk can't possibly hold that much memory.I'm thinking on an analogy to a bank that tells its customers they can each take out loans of 1,000 gold bars. They give their customers a note saying they have 1,000 gold bars worth of funds. Now say that the customers have used their loans to obtain different goods which they want to store in the bank. The bank would not be able to hold all those goods, and the people (processes) wouldn't be able to hold those goods either since once a computer is shut off all the memory not on disk is volatile. In a sense the bank is offering more than it can really hold.For a more practical example, say I have 1GB of disk memory available and my virtual memory system is able to virtualize 3GB of memory. Now say I open 3 text files and start typing stuff into them, eventually reaching that 3GB limit. Now I want to save those files, but I only have 1GB available on disk!Isn't virtual memory unreliable from a process point of view since it's saying I can store all this stuff for you but at the end of the day it doesn't have the resources to do so?
Is Virtual Memory unreliable?
computer architecture;operating systems;virtual memory