操作系统底层原理向来是计算机领域的硬骨头。几十万行内核源码摊在眼前，翻上几页便头晕目眩，既抓不住设计主线，更谈不上通篇精读。

egos-2000这个教学项目，只用2000行代码，就把操作系统的核心组件完整呈现了出来。

这套系统的三层架构尤其清晰： 底层直接管控硬件交互 中间层处理进程调度与系统调用 上层实现文件系统和命令解释器 它还能跑在QEMU模拟器和真实RISC-V开发板上，官方配套教材直接给出9个课程项目，方便边学边练。

操作系统从加电到用户界面究竟如何运转？这份源码就是最好的解剖样本，值得静下心一行一行啃透。 https://github.com/yhzhang0128/egos-2000…

yhzhang0128/egos-2000

Source: https://github.com/yhzhang0128/egos-2000

Vision

This project’s vision is to help every student read all the code of a teaching operating system.

With only 2000 lines of code, egos-2000 implements every component of a teaching operating system that runs on both QEMU and RISC-V boards. The EGOS book contains 9 course projects based on egos-2000.

# The cloc utility is used to count the lines of code.
> cloc egos-2000 --exclude-ext=md
...
github.com/AlDanial/cloc v 1.94  T=0.05 s (949.3 files/s, 62349.4 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                               30            453            677           1592
C/C++ Header                     9             64            105            258
Assembly                         3             14             46             92
make                             1             17             10             58
-------------------------------------------------------------------------------
SUM:                            43            548            838           2000 (exactly!)
-------------------------------------------------------------------------------

Earth and Grass Operating System

The “egos” part of egos-2000 is named after its three-layer architecture.

• The earth layer implements hardware-specific abstractions.
  • tty and disk device interface
  • timer and memory management interface
• The grass layer implements hardware-independent abstractions.
  • process control block and system call interface
• The application layer implements file system, shell, and user commands.

The definitions of struct earth and struct grass in the header file egos.h specify the layer interface. Please read USAGES.md for running egos-2000, and the instruction set manuals for the RISC-V privileged ISA.

Acknowledgements

Many thanks to Meta for a Facebook fellowship. Many thanks to Robbert van Renesse, Lorenzo Alvisi, Shan Lu, Hakim Weatherspoon and Christopher Batten for their support. Many thanks to Cheng Tan and Yu-Ju Huang for providing valuable feedback on the EGOS book and using egos-2000 in Northeastern CS4973/6640 and Cornell CS4411/5411. Many thanks to Haobin Ni and Hongbo Zhang for porting egos-2000 to mriscv, a simple processor written in SystemVerilog. Many thanks to Brandon Fusi for porting egos-2000 to Allwinner D1 and Sipeed’s Lichee RV64 Nezha compute module. Many thanks to Zack Light for making a YouTube video introducing egos-2000, and many thanks to Christopher Allison for making the DOOM video game work on egos-2000.

For any questions, please contact Yunhao Zhang.