December, 2024

Writing an OS Kernel from Scratch | Keyboard — How Keystrokes Become Characters Have you ever wondered about this process: you press a key → a character appears on screen. What does the OS experience in between? How do keyboard scan codes become scancodes? What’s the difference between USB HID and PS/2? From the mechanical... » read more

#233 Conntrack: High-Performance Connection Tracking and NAT Implementation Preface In the previous two articles, we thoroughly understood Netfilter’s HOOK mechanism (Article 231) and iptables’ rule table-chain system (Article 232). However, there’s one system hiding between them, omnipresent yet not yet detailed — Connection Tracking (conntrack). Conntrack is the cornerstone of Linux stateful firewalls. It’s because... » read more

B02 — The ID Card of RAM: What’s Actually Stored in the SPD Chip Key insight: RAM without SPD is like a person without ID — the system doesn’t know who it is. SPD Chip Basics Every DDR memory module has an SPD (Serial Presence Detect) chip, a 256-byte (or 512-byte for DDR5) EEPROM. SPD... » read more

Writing an OS Kernel from Scratch | #345: USB Protocol — From HID to High-Speed Devices Abstract: USB is essentially the “universal serial bus” for all peripherals, but many only know “plug and play.” This article takes you from physical layer topology, transfer types, xHCI controller, to practical lsusb usage, thoroughly understanding USB’s design philosophy... » read more

Writing an OS Kernel from Scratch – Part 7: User-Mode Processes and System Calls — Make Your OS Truly Usable! “No matter how powerful the kernel, if it can’t run user programs, it’s just a fancy bare-metal toy. Today, we embrace user mode, taking the decisive step toward becoming a true OS!” In the previous... » read more

Writing an OS Kernel from Scratch | The Last Jump from BIOS to Kernel — What the CPU Thinks After POST You press the power button, the screen lights up, the fan spins, BIOS POST completes, GRUB countdown ends — then what? How does the kernel actually start running? What state is the CPU in... » read more

B07 — From e820 to Memory Management Initialization: The memblock Allocator Key insight: The kernel’s first step at boot is to figure out how much memory it has to manage. How the Kernel Gets Memory Info At boot, the kernel obtains physical memory info through two methods: Directly from BIOS (legacy): via INT 15h E820h... » read more