In this lesson, you will learn about the persistence in storing data that​ is critical to the operating system.

We'll cover the following

The third major theme of the course is persistence. In system memory, data can be easily lost, as devices such as DRAM store values in a volatile manner; when the power goes away or the system crashes, any data in memory is lost. Thus, we need hardware and software to be able to store data persistently; such storage is thus critical to any system as users care a great deal about their data.

The hardware comes in the form of some kind of input/output or I/O device; in modern systems, a hard drive is a common repository for long-lived information, although solid-state drives (SSDs) are making headway in this arena as well.

The software in the operating system that usually manages the disk is called the file system; it is thus responsible for storing any files the user creates in a reliable and efficient manner on the disks of the system.

Unlike the abstractions provided by the OS for the CPU and memory, the OS does not create a private, virtualized disk for each application. Rather, it is assumed that oftentimes, users will want to share information that is in files. For example, when writing a C program, you might first use an editor (e.g., Emacs) to create and edit the C file (emacs -nw main.c). Once done, you might use the compiler to turn the source code into an executable (e.g., gcc -o main main.c). When you’re finished, you might run the new executable (e.g., ./main). Thus, you can see how files are shared across different processes. First, Emacs creates a file that serves as input to the compiler; the compiler uses that input file to create a new executable file (in many steps — take a compiler course for details); finally, the new executable is then run. And thus, a new program is born!

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