your computer has physical memory

memory
868 204-PIN SODIMM DDR3 CE

physical memory has addresses, like O-8GB

but when your program references an address like Ox 5c69a2a2, that’s not a physical with memory address! It’s a virtual address.

every program has its own virtual address space

program 1: Ox 129520 → “puppies”
program 2: Ox 129520 → “bananas”

Linux keeps a mapping, from virtual memory pages to physical memory pages called the page table

a “page” is a 4kb or chunk of memory (or sometimes bigger)

PID – virtual addr – physical addr
1971 – Ox 20000 – Ox 192000
2310 – Ox 20000 – Ox 228000
2310 – Ox21000 – Ox 9788000

when your program accesses a virtual address

CPU: I’m accessing Ox21000
MMU “memory management unit” (hardware): I’ll look that up in the page table and then access the right physical address

every time you switch which process is running, Linux needs to switch the page table

Linux: here’s the address of process 2950’s page table
MMU: thanks, I’ll use that now!