From: Tarik Nesh-Nash (tarikn_at_microsoft.com)
Date: Mon Mar 01 2004 - 17:18:24 PST
Computer hardware innovation advanced while the necessary corresponding
software and operating system were not capable to fully utilize the new
offered functionalities. This paper presents an easy and economical way
to support new hardware with a minimum of software changes.
The Virtual Machine Monitor inserts an additional thin layer between the
operating system and the hardware. This implementation solves many
problems, mainly, it keeps the compatibility and the reliability of
existing operating system, minimizes the overhead as in traditional
virtual machines also enhances resource sharing across the VMs. This is
also enabled with a very low cost comparing with a change or
implementation of the operating system and a minimum risk of bugs. The
DISCO implementation, in addition, controls the shared memory regions
and enable specialized operating systems, it is also able to manage
multiple copies of the same operating system and multiple OSs running
concurrently; and handles scalability and fault containment. However,
VM has face many problems mainly the memory and time overhead of
hardware resources, the difficulty of resource management since it is
controlled by the low level hardware and communication and sharing
between virtual machines.
The prototype Disco implements a layer of indirection between the
different resources (CPU, physical memory and i/o devices) and offers
methods of sharing (copy on write and virtual network interface), so it
is easy to run commodity OS or specialized systems (e.g. Splahos) with a
minimum implementation effort and minor changes to the OS.
The Disco performance is very good since the virtualization overhead is
not considerable.
This paper has a lot of clear implementation details that makes it
simple and easy to read.
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