That's not actually what's happening. When you allocate memory that needs to be initialized to zeroes, it doesn't actually allocate memory and zero it. Nor doe

That's not actually what's happening. When you allocate memory that needs to be initialized to zeroes, it doesn't actually allocate memory and zero it. Nor does it allocate memory without mapping the pages, and when a page fault occurs, allocate and zero it. Here's what actually happens. Upon boot up, the OS allocates a page, zeros it, and marks it read only. When pages are requested in the future that need to be zero, it assigns an address and maps the zero page to it. This zero page could be mapped to hundreds, thousands of pages. If you try to read from the page, it happily tells you it contains zeroes. So you still haven't allocated new physical pages to that address, despite the fact that you're actively using it. Only when you try to write to it does a page fault happen. (because you're trying to write to a read only page) Then it allocates a new page of physical RAM, zeroes it, and gives you a real physical page to use. It's clever hacks and abstractions all the down.