This article explains the fundamental differences between user mode and kernel mode in Linux, why the separation matters for security and stability, how mode switches occur via system calls, interrupts, and traps, and provides practical code examples and performance‑optimizing techniques such as zero‑copy and asynchronous I/O.
The article explains how frequent user‑kernel mode switches in Linux create hidden performance bottlenecks, describes the underlying privilege mechanisms on x86 and ARM, details the three switch triggers (system calls, hardware interrupts, traps), and provides practical optimization techniques such as reducing syscalls, using zero‑copy APIs, async I/O, DPDK, and kernel‑module examples to improve throughput.
The article explains how storage media speed, kernel and user mode separation, and context‑switch overhead affect I/O performance, then details DMA, zero‑copy methods such as mmap + write and sendfile, the role of PageCache, and best practices like async and direct I/O for large‑file transfers.
A nostalgic narrative explains how low‑level hardware control led to the invention of system calls, kernel/user modes, and ultimately the operating system concept, illustrating the transition from direct hardware manipulation to abstracted library functions.
This article explains the basic concepts of operating systems, covering their role as a hardware abstraction layer, the distinction between kernel and user modes, and how OS resource management (time‑sharing and space‑sharing) enables multiple programs to run safely and efficiently.
