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One of the biggest disadvantages of using type-safe languages and frameworks such as Java for the implementation of commercial operating system (OS) plat- forms is the lack of backward compatibility with legacy execution environments. Traditional Java operating systems are designed to execute Java programs. They struggle to support established application programming interfaces such as POSIX or Win32 as these are founded on the idea of direct execution of native machine code. Instead of using the host processor to execute legacy applications – which would eliminate most of the security and portability benefits of using a type-safe language for the OS implementation in the first place – we propose using a vir- tual processor implemented on top of the virtual machine infrastructure to execute legacy applications.

The recent surge in security exploits for the Microsoft Windows platform [5] demon- strates the need for foundationally safe operating systems (OSs) in internet-based com- puting. Language-based security is a promising new approach to rid applications from buffer-overflows, format string attacks and similar vulnerabilities. Currently, type-safe languages such as Java or C# are predominantly used in application code. Operating systems continue to be implemented in unsafe languages such as C or C++. To offer a viable alternative to the established operating system platforms Windows, Linux, etc., Java-based OSs need to learn to support the execution of legacy applications. Exist- ing implementations such as JavaOS [6], JX [3], or JOS [4] implement the majority of OS code in type-safe Java code, but allow to execute Java applications only. Em- ulating Java-based Application Programming Interfaces (APIs) on top of a Java OS is simple and has been successfully demonstrated by many Java-based OS implementa- tions. However, the vast majority of existing applications are written in type-unsafe languages and many of them are available as target-machine specific executables only. Being able to execute such applications on top of a Java-based OS would allow users to switch to a Java-based platform even before all applications have been ported.