Helios builds upon Singularity, the managed-code OS written by Microsoft
Research, in order to take advantage of heterogeneous platforms. Heterogeneous
computers have more than one programmable processor, often with diverse
instruction sets and different performance characteristics. Graphics cards are
a common example today, though they are are not generally programmable (unlike
the more recent GPGPUs). Other examples include NICs and HDDs with CPUs in them
to offload certain I/O processing tasks. Helios brings together
microkernel-style message passing APIs, Singularity safety, and the platform
independence of Microsoft's Common Intermediate Language (CIL). Message passing
gives a unified interface for IPC, I/O, and other tasks/services provided by the
OS and subsystems. The OS and user code is written in managed code that is
garbage collected and verified to be typesafe at compile time and run time. This
means that all code in the system can be run in the same address space in
privileged mode: context switches can be very cheap. The CIL allows for
application and kernel code to be compiled once and then run (by the virtual
machine) on many different architectures without having to resort to fat
binaries.

The novel aspects of this paper are that the extra processors execute their own
"satellite kernels" that manage their own timers, interrupts, resources, and
processes. In effect, the computer becomes a distributed system where kernels
communicate with each other over (very reliable) interconnect busses like
PCI-Express. The message passing API stays the same, so that processes on
different kernels can communicate with simple calls. This style of remote
message passing is more expensive than local message passing between processes
on the same processor. To avoid as much overhead as possible, Helios lets the
user specify "affinity" of a process relative to a platform and other processes
by changing an XML metadata file. This can be done without needing to recompile
the executable. I think this is a sustainable approach for facilitating the use
of heterogeneous, multi-processor computer systems as they become more common.
The creators of Helios look forward to being able to port their OS to Intel's
Larrabee graphics processor. They would also like to be able to port a commodity
OS like Windows to their model, so that more experiments can be run on a greater
variety of software.