VIRTUAL MACHINES:
·
Creating an abstract of a single computer
(hardware) into several different execution environments, thus creating the
illusion that each separate execution environment is running its own private
computer.
·
By using CPU scheduling and virtual
memory techniques OS can create illusion that a process has its own processor
with its own memory
·
Virtual machine approach does not
provide any additional functionality but provides an interface that is
identical to the underlying hardware
The resources
of the physical computer are shared to create the virtual machines.
1. CPU scheduling can create the appearance that users have their own
processor.
2. Spooling and a file system can provide virtual card readers and
virtual line printers.
3. A normal user time-sharing terminal serves as the virtual machine
operator’s console.
Advantages/Disadvantages of Virtual Machines
·
The virtual-machine concept provides
complete protection of system resources since each virtual machine is
isolated from all other virtual machines.
·
This isolation, however permits no
direct sharing of resources.
·
A virtual-machine system is a perfect vehicle
for operating-systems research and development.
·
System development is done on the virtual machine,
instead of on a physical machine and so does not disrupt normal system
operation.
·
The virtual machine concept is difficult to implement due
to the effort required to provide an exact duplicate to
the underlying machine.
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