Memory management & virtual memory

Main memory is small and processes are big, so the operating system must share it fairly and safely. Paging solves the sharing problem elegantly: memory is split into fixed-size frames, each process is split into same-size pages, and any page can live in any frame — so there is no external fragmentation, because no hole is ever the wrong size. Worked example: with a 4 KB page size, a 32-bit logical address splits into a 20-bit page number and a 12-bit offset, because 4 KB = 2^12 bytes. The offset never changes during translation; only the page number is looked up in the page table. That single fact — offset passes through unchanged — answers many address-translation questions.