introduction
The concept of virtual machine is not new for computer world, but many people don't know or understand this concept. If you are a typical computer user, and through the Internet, browse the web page, then you are likely to interact with a virtual machine, this virtual machine is a Java virtual machine. Now, since this virtual machine is transparent to most of the computer users, you may be confused: Why do you care about the virtual machine, right? In fact, in the computer world, the concept of virtual machines is often used to solve some very important issues. But usually this
These purposes of all virtual machines are very important for our calculations today. Some are transparent to users because virtual machines are generally used inside users and operating systems that users use daily. The problem to be solved by the virtual machine includes: sharing the same hardware by splitting hardware, making the software "portable" between multiple operating systems, and running old software on new computers. These purposes of all virtual machines are very important for our calculations today. With the in-depth reading, we will show you how virtual machines help solve these important problems, so that you can understand why virtual opportunities become an important part of modern computers. When we try to explain the concept of virtual machines, we must first understand the concept of "virtual". The word "virtual" is the earliest to optics, used to understand objects in the mirror. The object in the mirror is an image of a practical physical existence, but it is not a real object. This means that this image looks exactly the same as the actual object, and in the same location. Now, the word "virtual" has evolved to describe any simulation of any real object, such as virtual memory, virtual disk, and virtual reality. When we discuss the virtual machine, we use the word "virtual" because we want the virtual machine to look and work, all of the real machine is exactly the same. This means that the virtual machine is not a real machine, but he can work like a real machine. Now, when defining the word word, we have used the word "simulation". Simulation
The simulation is those used to mimic other things. It is those things used to imitate other things. A very good example of simulating modern applications is the training of Air Force and Navy Pilots. The pilot is trained on the flight simulator: the computer-based machine, it looks like a cockpit of a jet. Such a machine, so that the driver does not have to leave the ground, you can feel the same feeling like a real jet plane, and see the same thing. This simulator imitates everything from the actual performance of the aircraft, air and weather conditions on the flying aircraft. Basically, the simulator allows the pilot to be able to get all the skilled and feels that drive a truly jet aircraft can be obtained. The concept of simulating or imitating another thing is introduced into the design of the computer system. Although the virtual machine has a lot of incarnation,, from his most essential level, a virtual machine is a representative of the machine that does not actually exists. This is of course the most general, it is also very unclear. But I will endure it with us. Now let's consider the most general concept of a machine. All machines, whether it is a refrigerator, a recorder, or a computer, there is a common point: they are designed to complete a specific set of instructions. These instructions form a set of instructions. Any machine's instruction set can be imagined into a box with LEGO (canie assembled toys). These LeGOs are placed together and make up a whole. For machines, these Lego is instructions, they are used to tell the machine what to do, and what tasks are done. For virtual machines, "virtual" actually refers to these instructions. The virtual machine has many different types, but they have a common topic that simulates the concept of an instruction set. Each virtual machine has a user accessible instruction set. The virtual machine maps these virtual instructions "mapping" to the actual instruction set of the computer. This mapping relationship is shown in Figure 1.1: In the field of virtual machine, there are four different ideological genre. The first IBM virtual machine model is represented, it is almost one one-one mapping. The second genre consists of a mapping between each instruction and a virtual instruction, which is represented by a Java virtual machine. The UNIX virtual machine model and the OSI virtual machine model represent the last two models. We will tell these models later. Both models map part of the directive, while other instructions are directly called the operating system function.
