What is a virtual machine?
“Virtual machine” is the term applied to the server environments running on a piece of hardware. So, in the example above, the decoupled Linux and Windows servers running on a single blade server would be referred to as virtual machines. How does virtualization work? Generally, server virtualization solutions work by introducing a thin layer over the physical server. This layer partitions the physical server into separate areas that the virtual servers then run on. Computing resources from the underlying server are viewed as a pool of resources which can then be shared among the virtual machines sitting on top. With the exception of that sharing of computing resources, each virtual server acts as its own entity; problems with an application on one server do not affect other virtual machines on that same physical server.
A virtual machine is a tightly isolated software container that can run its own operating systems and applications as if it were a physical computer. A virtual machine behaves exactly like a physical computer and contains it own virtual (ie, software-based) CPU, RAM hard disk and network interface card (NIC). An operating system can’t tell the difference between a virtual machine and a physical machine, nor can applications or other computers on a network. Even the virtual machine thinks it is a “real” computer. Nevertheless, a virtual machine is composed entirely of software and contains no hardware components whatsoever. As a result, virtual machines offer a number of distinct advantages over physical hardware.
A virtual machine is a type of computer application used to create a virtual environment, which is referred to as virtualization. Virtualization allows the user to see the infrastructure of a network through a process of aggregation. Virtualization may also be used to run multiple operating systems at the same time. Through the help of a virtual machine, the user can operate software located on the computer platform. There are several different types of virtual machines. Most commonly, the term is used to refer to hardware virtual machine software, also known as a hypervisor or virtual machine monitor. This type of virtual machine software makes it possible to perform multiple identical executions on one computer. In turn, each of these executions runs an operating system. This allows multiple applications to be run on different operating systems, even those they were not originally intended for. Through the use of the hardware virtual machine software, the user has a seemingly private
A virtual machine is the construct of a program (such as CP/370) that behaves so much like a real machine that an OS, or other program written to run alone on a real machine, is fooled into thinking that it is running on a real bare machine by itself! One way to do this is to simulate the hardware’s appearance to the software. The commercial products RealPC and Virtual PC run on a Mac and simulate an IBM compatible PC. Those programs must simulate each x86 instruction just as it would be executed by x86 hardware. (2003: Microsoft bought Connectix and the product survives as Virtual PC for Mac.) Now (2006) there is a VM for the Intel Mac. I presume they exploit Intel’s new virtualization features. There is a more efficient way if the machine that you would simulate is the same as the machine that you run on. If you have a zot why would you want to simulate a zot? Here are a few reasons: • Provide interactive debugging of privileged code, such as an operating system. On expensive machine
A “real computer” provides an operating system many things, including a CPU, I/O channels, memory, a BIOS to provide low level access to motherboard and I/O resources, etc. When an operating system wants to write to a hard drive, it communicates through a device driver that interfaces directly with the hardware device memory. However, it’s possible to give a program all the hardware resources it needs. When it wants to access a hard drive, give it some memory to write to. When it wants to set an IRQ, give it some bogus instructions that lets it think it set an IRQ. If you do this correctly, then in principle, there’s no way for the poor application to know whether it’s really accessing hardware or tricked by being given resources which simulate hardware. A virtual machine is the environment which tricks applications into believing they’re running on a real computer. It provides all the services that a real computer would provide. VM’s were used initially in the 1960’s to emulate time s
