New MSIM homepage is at

Documentation can be found at while source code is at

Introduction MSIM

To develop an operating system from scratch is an invincible problem for most students – but starting at already finished base will never disclose them what the operating systems are about.

MSIM is a light-weight computer simulator based on MIPS R4000. It is used for education and research purposes, mainly to teach the construction and implementation of operating systems. MSIM is distributed with source code under the GNU GPL license to make possible modifications for users and works on most POSIX-compliance environments (mainly GNU/Linux, Mac OS X, but can be also compiled in Cygwin or MinGW in Windows). The user interface is simple terminal-style.

MSIM provides following features (along others):

MSIM does not aim to be a speed-optimized real hardware simulator, but rather a fully deterministic simulator useful for kernel debugging. There are several other projects which aim speed-optimized simulation (e.g. GXemul), but they are more complex to use.


If you have any ideas for improvements, feel free to contact us. In the case you have found a bug, please let us know via email. Attach the configuration, binary images and a detailed description of the bug so we can reproduce it.


The current version is

Download MSIM [165 kB]

Martin Decky
Viliam Holub