Virtual Machines Essay

1840 Words 8 Pages
(1)Virtual Machines
The fundamental idea behind a virtual machine is to remove the hardware of a single computer and make it a self-contained operating environment that behaves as it is a separate computer. Essentially, the virtual machine is software that executes an application and isolates it from the actual operating system and hardware. CPU scheduling and virtual-memory techniques are used so that an operating system can create the illusion that a process has its own processor with its own (virtual) memory. The virtual machine provides the ability to share the same hardware yet run several different operating systems concurrently, as shown in Figure 2-11.
Figure 2-11: Virtual machine concept
A major difficulty with the virtual
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There are several advantages with the virtual machine concept. In this environment, the various system resources have complete protection. Each virtual machine is completely isolated from all other virtual machines, so there are no protection problems because there is no sharing of resources. Two approaches have been implemented to provide sharing. First, it is possible to share a virtual disk to share files. This is modeled after a shared physical disk is implemented by software. Second, it is possible to define a network of virtual machines, each virtual machine sending information over the virtual network. This is modeled after physical networks, but is implemented in software.
The virtual machine system is perfect for operating system research and development. Typically, changing an operating system is a difficult and time consuming task. This is because operating systems are quite large and complex programs and it is difficult to be sure that a change in one part of the system will not cause problems (or bugs) in another part of the system. The complexity and power of the operating system makes it dangerous to change it because the operating system executes in kernel mode. Therefore, a wrong change could cause an error that could destroy the entire file system. This is why it is crucial to test all changes to the operating system carefully and thoroughly.
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