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This page discusses the JOS kernels and their development status.

Status [05-13-99]

+ The JJOS and RJK kernels are in early early early alpha. They boot, and "say hello" but still have major rough spots to iron out before they are ready for a beta. More info about the JJOS kernel is available on the decaf page.
++ The Simple kernel is being considered by Geoff O'Callaghan and RobertFitzsimons. "SimpleJOS" is not the name of this kernel, simply a place holder until they decide if they are going to build it, and what its name will be.

The Kernels

JOS has 2 1/2 kernels under development. These kernels are:


JJOS is being built "from the top down". The design centers around the decaf Java Virtual Machine ( JVM ) with JJOS simply providing hardware abstraction for decaf. This should result in a simple, efficient design. Stress is being placed on keeping JJOS as minimal as possible (both in size and functionality).

Most of the OS will be written in Java. Portability will be maintained by minimizing JJOS so that it can be easily ported to other platforms. decaf and the Java implemented portions of the resulting operating system will then work with no changes on other platforms.


Robert's JOS Kernel ( RJK ) is a microkernel designed to comply with the KernelInterface architecture. It does not implement a jvm. Instead, a jvm will need to be built or ported to the RJK. Since RJK is designed to provide a generic microkernel, it is hoped that this design will provide an easy plug-in architecture. The whole OS based on RJK will therefore be very flexible and easily customizable.


The SimpleJOS kernel is being discussed as a fast hack to give JOS developers a platform to test their JOS utitilies, applications, and games on _now_!

There have been some worries that the current kernel progress is too slow. To provide a stepping stone to a finished custom JOS operating system, it is proposed that linux or freebsd be trimmed down, and customized (by adding an opensource JVM, and supporting utilities) to be a testbed JOS operating system. This method will get us an OS quickly but most of the OS will be written in C and follow traditional OS design (which is counter to the JOS goal of writing most of the traditional OS code in Java).

A Kernel does not an Operating System make

That's Yoda-speak for, "An operating system is more than just a kernel". The kernel will only provide the most basic services for the operating system. Many utilitis and tools are needed to make the kernel usable. This combination of the kernel, its drivers and "modules", and utilities together form a complete Operating System. Many JOS projects are actively working on creating these supplementary tools. See the ProjectList and appropriate sections of the GettingStartedProducts page for more information.

This is a work in progress. I've created a skeleton but if anyone knows more, please supplement the above. Also, comments are greatly appreciated. Add those below (with your name and date please).

- IainS [05-13-99]


The CjOS kernel is similar to the JJOS kernel, in that it will be created from scratch and boot-able from Etherboot and GRUB. See also the CjOSPages article. -- GilbertHerschberger (6 February 2001)

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