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A number of people noticed that they can create a virtual machine with four virtual processors, and then successfully run Windows XP on it and have it utilize all four virtual processors. This strikes them as odd, because Windows XP supposedly only supports the use of one or two processors in a computer.
To understand what is happening we need to talk about processor topology.
A long time ago, the universe used to be quite simple. When you talked about a processor you meant a physical chip that you put inside a computer that was capable of handling one stream of execution. Then along came concepts such as hyper threading and multi core processors. These technologies allow a single physical processor to handle multiple streams of execution, and effectively appear like multiple physical processors.
In this new world, in order to differentiate between the physical chip that you put in a computer and a single stream of execution on the chip, we use the terms "package", "socket" or "physical processor" to refer to the actual physical chip that you put inside the computer. And the term "logical processor" to refer to a single thread of execution on the chip.
"Processor topology" is simply the ratio and nature of logical processors to physical processors in a computer.
This all gets interesting when it comes to the question of how virtual processors are represented inside of a virtual machine.
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