S09 — ECC Memory: How Single-Bit Errors Are Detected and Corrected Key Insight: A reliable system is one that can still operate correctly under the worst conditions. Two Types of Memory Errors: Error Detection vs. Error Correction Memory errors fall into two categories: Bit Flip: Physical causes: - Cosmic rays (high-energy particles) hitting a DRAM... » read more

H07 — How DDR Power Consumption Is Calculated: IDD Parameters and Power Models Key Insight: Every refresh, every activation, every read and write consumes power. Components of DDR Power Consumption DDR memory power consumption has three parts: Static Power (Leakage) + Dynamic Power (Switching) + I/O Power. DDR 系统功耗分解： 1. 核心功耗（Core Power）： - DRAM Cell... » read more

Writing an OS Kernel from Scratch | System Calls — How User-Mode Triggers Kernel Code You wrote a single line write(fd, "hello", 5); in your program. This is just a C function call inside libc — how does it make its way step by step to the kernel, ultimately writing characters to the screen or... » read more

Writing an OS Kernel from Scratch | 349: SPI Bus — High-Speed Serial Communication Abstract: SPI is a higher-speed serial bus compared to I2C, commonly used with Flash storage, displays, sensors, and more. This article details SPI’s four modes, protocol timing, the Linux spidev driver, and its application in Flash storage. 1. SPI Protocol: Four-Wire... » read more

# Writing an OS Kernel from Scratch – Part 29: Mouse Driver — Adding Pointer Control to Your GUI “The keyboard is efficient, but the graphical interface can’t do without a mouse. Today, we implement a PS/2 mouse driver, enabling your window manager to support clicking and dragging!” In the previous article, we implemented a... » read more

S10 — How to Read a Memory Datasheet Key Insight: Engineers who can read a datasheet can make correct product decisions. Basic Structure of a Datasheet A memory datasheet typically contains the following main sections: Typical memory datasheet structure: 1. Overview - Capacity, model number, voltage, package 2. Architecture - Organization (e.g., 1G × 8,... » read more

H03 — CL-tRCD-tRP-tRAS: How Memory Timings Affect Actual Latency Key Insight: Choosing memory only by rated frequency is like buying a car only by top speed. You’ll miss a lot. What Are Memory Timings Memory timings are parameters describing delays between memory commands. They collectively determine how fast memory operations are. DDR4 主要时序参数（以 DDR4-3200 CL22... » read more

# Writing an OS Kernel from Scratch – Part 30: Window Manager Mouse Support — Implementing Click, Drag, and Window Operations “The keyboard is efficient, but the mouse is intuitive. Today, we integrate mouse support into the window manager, achieving true graphical interaction!” In the previous article, we successfully implemented the PS/2 mouse driver and... » read more

A07 — Memory Pool: Pre-allocate, On-demand Allocation, Avoiding Fragmentation Key Insight: In scenarios with frequent allocation/deallocation, pre-allocating a pool is 100x faster than asking the system each time. What is a Memory Pool A Memory Pool pre-allocates a large block of memory and allocates from it on demand. Compared to calling malloc each time, memory... » read more

H10 — The Memory Controller Inside the CPU: IMC Architecture and Core Interaction Key Insight: The best memory control makes the CPU unaware of latency. Location of the Memory Controller (IMC) The Memory Controller is the bridge between the CPU and DRAM. Modern CPUs integrate the IMC on the CPU die. CPU 芯片架构（以 Intel Skylake... » read more

K07 — The Story Behind malloc: brk, mmap, and the ptmalloc Allocator Key Insight: The malloc you call hides a complete allocator system behind it. It is more complex than you think. malloc Is Not a System Call Many people think malloc is a system call. In fact, malloc is a glibc library function. It... » read more

332 – Android init Process: The First Userspace Process Series Navigation: 330-Boot Overview | 331-Bootloader | 333-Zygote Two articles ago, we covered how the Bootloader loads the kernel. Last time, we covered how the kernel decompresses, initializes hardware, and jumps to execute userspace code. Now we arrive at a pivotal role in the Android boot... » read more

Writing an OS Kernel from Scratch | 346: Keyboard — How Keystrokes Become Characters Abstract: You press a key, and a character appears on screen — what happens in between? This article traces the complete data path of keyboard input, from hardware matrix scanning, PS/2 protocol, USB HID descriptors, to the Linux input subsystem. wandos... » read more

Understanding Low-Level Principles – Memory Series | S04 | Complete DRAM Access Timing: Commands, Signals, and the Source of Latency Key Insight: The journey of data from Cell to CPU core is etched in every step on the timing diagram. Read the timing diagram, and you’ve read half of DRAM. 1. DRAM Command and Signal... » read more

232 iptables: Deep Analysis of Rule Tables and Chains Preface In the previous article, we gained a deep understanding of Netfilter’s HOOK mechanism — that’s the underlying infrastructure of the entire framework. If we think of Netfilter as the ramp system of a highway, then iptables is the rulebook at the toll booths on those... » read more

356 | System Calls: How User Mode Triggers Kernel Code Key Insight: User programs can never directly read or write hardware. Even just printing a character requires asking the kernel to do it on their behalf. System calls are the only gateway for this “proxy” service. 1. Problem: What If a User-Mode Program Wants to... » read more

Writing an OS Kernel from Scratch | Windows GPT+UEFI Boot: ESP Partition, NVRAM Boot Entries, and Secure Boot — Complete Analysis The previous chapter covered the Windows boot chain in MBR+BIOS mode. The System Reserved partition was the core anchor of the entire chain — BOOTMGR and BCD both resided in that 100MB FAT32 partition,... » read more

Writing an OS Kernel from Scratch | Process and Scheduling — From fork to schedule, How a Process is Born You press ./a.out and hit Enter — a process starts running. How is this process “created” by the operating system? What does fork do? What does exec do? How does the scheduler decide which process... » read more

# 05: Memory Management – User Mode: From brk to malloc — Deep Dive into User-Space Memory Allocators “When a user program calls malloc, how do the kernel and libc work together? This article delves into the brk/mmap system calls, the dlmalloc algorithm, and compares glibc’s implementation details, building an efficient, low-fragmentation user-space memory allocator.”... » read more

358 | Timer: HPET and Clock Interrupts Key Insight: The operating system’s sense of time doesn’t come from “watching a clock” — it’s “punched out” by interrupts. Each clock tick tells the kernel that another jiffy has passed — and then it decides who gets to run next. 1. Three Clock Hardware Components The x86... » read more