How to Overcome the Cold Start: A Minimalist OS Learning Roadmap

Cold Start

For beginners with little or no computer‑system background, the biggest obstacle is the "cold start" – not the amount of code but the lack of a clear entry point. The author recommends the book 30 Days to Build an OS , which presents a friendly, step‑by‑step path but suffers from Japanese‑language comments in the source code and custom tooling that limits portability.

Early Stage

After achieving a simple "hello world" or basic thread‑switching demo, readers need to move beyond hand‑holding and understand general OS principles. The book Operating System Truth Restored is suggested; it covers topics such as what an OS is, how software accesses hardware, memory segmentation, flat memory model, and kernel traps. Important questions from the book are highlighted in a blockquote.

0.1 What is an operating system 0.2 What depth of study you aim for 0.3 What tasks you must implement yourself 0.4 How software accesses hardware 0.5 What applications are and how they cooperate with the OS 0.6 Why we talk about “traps” into the kernel 0.7 Why memory is divided into segments 0.8 What a flat memory model is

Middle Stage

At this point the learner starts exploring real‑world kernels. The author read The Art of Linux Kernel Design and Linux Kernel Complete Annotations while examining the source of Linux 0.11. A short excerpt from main.c is shown to illustrate the low‑level hardware interaction code.

#define CMOS_READ(addr) ({ \
    outb_p(0x80|addr,0x70); \
    inb_p(0x71); \
})

#define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10)

static void time_init(void)
{
    struct tm time;
    do {
        time.tm_sec = CMOS_READ(0);
        ...
    }
}

The author also tried to rewrite parts of the kernel, simplifying memory layout (hard‑coding 32 MiB) and limiting disk support to a single drive to reduce complexity.

Later Stage

Having grasped the overall OS architecture, the author chose to stop further deepening because his primary job is Java development, not full‑time kernel engineering. He emphasizes that continued study is optional and should be driven by personal interest and available time.

My Experience Summary

Cold Start : 30 Days to Build an OS

Early Stage : Operating System Truth Restored

Middle Stage : The Art of Linux Kernel Design, Linux Kernel Complete Annotations, Linux 0.11 source

Later Stage : stopped

Planned Minimalist OS Tutorial

The upcoming series aims to provide a concise, high‑density tutorial that bridges the gap between massive textbooks and overly brief online articles. It will outline the core OS workflow, essential knowledge, required steps, and psychological barriers, offering frequent positive feedback to keep readers engaged.

Gift: Simple OS Demo

A tiny demo that runs on Windows without any environment setup; the source code is available at https://gitee.com/sunym1993/flash-4th-os.git.