How does the operating system allocate and free pages in virtual memory in Windows?

[ProfRon]

You ever wonder how Windows juggles all that memory without crashing your apps? It treats memory like a giant puzzle, breaking it into small chunks called pages. When your program needs space, the OS grabs some virtual room first. It promises that space exists, even if it's not physical yet.

I mean, think of it as the OS playing matchmaker between your code and actual RAM. If RAM's full, it swaps pages to the hard drive temporarily. You launch a game, and boom, pages get allocated on the fly. The OS checks if those pages are free or in use elsewhere.

Frees up nicely too, once you're done. Your app closes a file, and the OS marks those pages as available again. It might even shuffle them around to make room for hotter stuff. No big drama, just quiet housekeeping in the background.

Sometimes it pages out idle bits to disk, freeing physical spots for urgent tasks. You multitask like crazy, and Windows decides what to tuck away. It tracks everything with hidden maps, so nothing overlaps by mistake.

Pages come in fixed sizes, usually four kilobytes each. The OS allocates them lazily, only when you touch the memory. You write some data, and it pulls a page from the pool right then.

Freeing happens in reverse, almost sneaky. The OS notices unused pages and recycles them fast. It coalesces fragments to keep things tidy for next time.

If pressure builds, it trims working sets from background apps. You feel it when things slow, but the OS prioritizes your foreground fun. It even commits pages only after reservation, avoiding overpromises.

Swapping back in is quick if the page lives on disk. The OS fetches it when demanded, no questions asked. You scroll through photos, and pages flip in seamlessly.

This whole dance keeps your system humming without you noticing. It allocates fresh pages for new loads, frees the stale ones without fuss.

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