Adaptive Domain Environment for Operating Systems
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Adeos (Adaptive Domain Environment for Operating Systems) is a nanokernel hardware abstraction layer (HAL) or a hypervisor that operates between computer hardware and the operating system that runs on it. It is distinct from other nanokernels, in that it is not just a low level layer for an outer kernel. Instead it is intended to run several kernels together, which makes it similar to virtualization technologies.
Adeos provides a flexible environment for sharing hardware resources among multiple operating systems, or among multiple instances of a single OS, thereby enabling multiple prioritized domains to exist simultaneously on the same hardware.
Adeos has been successfully inserted beneath the Linux kernel, opening a range of possibilities, such as SMP clustering, more efficient virtualization, patchless kernel debugging and real-time systems for Linux.
Unusually among HALs, Adeos can be loaded as a Linux loadable kernel module to allow another OS to run along with it. In fact Adeos was developed in the context of RTAI (Real-Time Application Interface) to modularize it and to separate the HAL from the real-time kernel.
There are two categories of existing solutions that enable multiple operating systems to run on the same system. The first is simulation-based and provides a virtual environment for which to run additional operating systems. The second suggests the usage of a nanokernel layer to enable hardware sharing.
In the simulation category there are tools such as VMware, Plex86, VirtualPC and SimOS. There is also KVM which is more similar to Adeos but is not RT and requires specific virtualization hardware support. These solutions are used for users who desire to run applications foreign to their base OS, they provide no control whatsoever over the base OS to the user. Simulation was never meant to be used in a production environment. In the nanokernel category there are tools such as SPACE, cache kernel and Exokernel. All of these suggest building miniature hardware management facilities which can thereafter be used to build production operating systems. The problem of this approach is that it does not address the issue of currently existing operating systems and their user base.
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