Operating System Concepts

Learning Objectives Differentiate between user mode and kernel mode. Explain the purpose and mechanism of a system call. Write a simple program that uses system calls for file input/output (I/O). Describe the basic lifecycle of a process (creation, execution, termination). Write a program that creates and manages a child process using fork() and wait(). Identify and handle common errors returned by system calls. Ever wondered how a simple `print()` statement in your code actually makes pixels light up on your screen? 🤔 Let's pull back the curtain and see how your programs talk to the operating system! This lesson explores systems programming, the art of writing software that interacts directly with the operating system's services. We'll learn how application...

TermDefinitionExample System CallA programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. It's the bridge between an application and the OS.When your program wants to read data from a file, it doesn't access the hard drive directly. Instead, it makes a `read()` system call, and the OS kernel performs the operation and returns the data. User Mode vs. Kernel ModeTwo distinct CPU modes of operation. User mode is a restricted mode where applications run, preventing them from directly accessing hardware or critical memory. Kernel mode is a privileged mode where the OS kernel runs, with unrestricted access to all hardware and memory.Your web browser runs in user mode. When you click 'Save As', the browser ma...

System Call Pattern for File I/O 1. Open: `fd = open(path, flags)` 2. Operate: `bytes = read(fd, buffer, count)` or `bytes = write(fd, buffer, count)` 3. Close: `close(fd)` This is the fundamental sequence for all file operations. You must first get a file descriptor from `open()`, then use it to read or write data, and finally release the resource with `close()` to prevent resource leaks. Process Creation with fork() pid_t pid = fork(); if (pid < 0) { /* error */ } else if (pid == 0) { /* child process code */ } else { /* parent process code */ } The `fork()` system call creates a nearly identical copy of the calling process. The key is to check the return value: it returns 0 to the new child process and the child's PID to the parent process. This allows you to writ...