Stack vs heap: what actually lives where

Fri, 31 Jul 2026 15:00:00 +0100

The stack and the heap are where almost all of a running program’s data sits. Most explanations of them are roughly right and specifically wrong, usually in the same four places. This is my attempt at getting it right, checked against a running VM rather than recalled.

Both are regions of a process’s virtual address space. They are backed by RAM, but a given page may be in cache, in RAM, or swapped to disk, and the addresses a program sees are virtual ones the operating system maps on its behalf. RAM is called volatile because it loses its contents without power. That is all the word means here — it is not a collective name for the regions a program runs in.

Fundamentals on Ahmed Kafi

Stack vs heap: what actually lives where