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Envision a future where every student can read all the code of a teaching operating system.


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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 an operating system for education. It can run on RISC-V boards and the QEMU software emulator.

Fail to load an image of egos-2000.

# The cloc utility is used to count the lines of code (LOC).
# The command below counts the LOC of everything excluding text files.
> cloc egos-2000 --exclude-ext=md,txt,toml,json
... v 1.94  T=0.05 s (949.3 files/s, 62349.4 lines/s)
Language                     files          blank        comment           code
C                               33            439            557           1588
C/C++ Header                     9             67             99            277
Assembly                         2              8             41             87
make                             1             15              4             48
SUM:                            45            529            701           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, exception 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 header file egos.h specify the layer interface. Please read for running egos-2000 and the instruction set manual for the RISC-V privileged ISA.


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 all the CS5411/4411 students at Cornell University over the years for helping improve this course. Many thanks to Cheng Tan for providing valuable feedback and using egos-2000 in CS6640 at Northeastern University. Many thanks to Brandon Fusi for porting to the Allwinner's D1 chip using Sipeed's Lichee RV64 compute module.

For any questions, please contact Yunhao Zhang.