9.5.6: Swapping

The solution to this problem lies in a technique known as .

Chapter Section: 9.5 Memory Management Subsection: 9.5.6 Swapping 1. Introduction to Swapping In the architecture of modern computer systems, Random Access Memory (RAM) is a finite, precious resource. The Central Processing Unit (CPU) executes processes only when they reside in main memory (RAM). However, the aggregate memory requirement of all active processes frequently exceeds the physical capacity of the installed RAM. This presents a critical challenge to the operating system: how to maintain execution flow without crashing the system due to memory exhaustion. 9.5.6 Swapping

While modern systems often rely heavily on paging and virtual memory, understanding swapping—specifically swapping entire processes—is fundamental to grasping how operating systems balance multiprogramming degrees against hardware constraints. Swapping consists of two primary operations. To understand these, one must visualize main memory as a container and the "Backing Store" (or swap space) as a holding area on the hard disk or SSD. 2.1 Swap-Out When the operating system detects that memory is running low or a higher-priority process requires space, it selects a process currently residing in RAM. This process is suspended, and its entire memory image—including the code, data segments, stack, and PCB (Process Control Block)—is copied to the backing store. Once the transfer is complete, the memory allocated to that process is freed, making it available for other processes. 2.2 Swap-In When the scheduler decides that a swapped-out process is ready to resume execution, the OS locates its memory image on the backing store. It then allocates a new block of free memory in RAM and copies the process back from the disk. Once loaded, the process is moved from the "suspended" state to the "ready" state. The solution to this problem lies in a technique known as

Swapping is a memory management scheme that temporarily moves a process (or part of a process) from main memory to secondary storage (disk) and brings it back into memory for continued execution. This mechanism allows the total physical address space of all processes to exceed the actual physical memory of the system, effectively creating an illusion of a larger memory pool for the user. The Central Processing Unit (CPU) executes processes only