Introduction to Virtual Machines (III.)--Introduction

Introduction


The concept of virtual machines is not new to the computer world, but many people do not know or understand the concept. If you're a typical computer user and you surf the web through the Internet, you're probably interacting with a virtual machine that is a Java virtual machine. Now that the virtual machine is transparent to most computer users, you may wonder why you care about virtual machines, right?

In fact, in the computer world, the concept of virtual machines is often used to solve some very important problems. But usually this


These uses of all virtual machines are very important for our calculations today.




Some are transparent to users because virtual machines are typically used within programs and operating systems that users use every day. The problems to be addressed by virtual machines include splitting the hardware so that many programs share the same hardware, making the software "portable" between multiple operating systems, and running old software on a new computer. These uses of all virtual machines are very important for our calculations today.

As reading progresses, we will show you how virtual machines can help solve these important problems, so that you understand why virtual opportunities are 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 originally derived from optics, used to understand objects in a mirror. The object in the mirror is an actual physical image, but it is not a real object. This means that the image looks exactly the same as the actual object and is in the same position. Now, the word "virtual" has evolved to describe the simulations of any real object, such as virtual memory, virtual disk, and virtual reality. When we talk about virtual machines, we use the word "virtual" because we want the virtual machines to look and work exactly the same as the real machines. This means that a virtual machine is not a real machine, but he can work exactly like a real machine.

Now, when we define the word virtual, we have used the word "impersonation". Simulation on




Simulation is the thing that imitates other things.




Are those things that imitate other things. A very good example of simulations in modern applications is the training of air and naval pilots. Pilots are trained on flight simulators: computer-based machines that look like the cockpit of a jet plane. This machine allows the driver to feel like driving a real jet plane without leaving the ground and seeing the same thing. This simulator mimics everything from the actual operational performance of the aircraft to the wind and weather conditions affecting the flying aircraft. Basically, the simulator allows the pilot to get all the skills and feel of driving a real jet on a safe ground.


The concept of simulating or imitating another thing is introduced into the design of computer systems. Although virtual machines have many avatars, a virtual machine is the representation of a machine that does not actually exist, from his most essential level. This is, of course, the most general and very unclear definition. But bear with us first.


Now, let's consider the most general concept of a machine. All machines, whether refrigerators, VCRs, or computers, have one thing in common: they are designed to accomplish a specific set of instructions. These instructions form a set of instructions. The instruction set of any machine can be imagined as a box equipped with Lego (high assembled toy). These Lego are put together to form a whole. For machines, these Lego are instructions, and they are used to tell the machine what to do and what tasks to accomplish.


For virtual machines, "virtual" actually refers to these instruction sets. There are many different types of virtual machines, but they have a common theme that simulates the concept of a set of instructions. Each virtual machine has a set of instructions that the user can access. Virtual machines "Map" These virtual instructions to the actual instruction set of the computer. This mapping relationship, as shown in Figure 1.1:












In the field of virtual machine, there are four different schools of thought. The first is represented by the IBM virtual machine model, which is almost a mapping. The second genre consists of a mapping between each instruction in the machine 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'll talk about these models later. These two models map directly to a subset of instructions, while others are direct calls to operating system functions.