IBM virtual machine model
In the IBM model, each virtual machine is a complete copy of the true machine, just a less memory.
The virtual machine of the IBM (International Business Machines) is one of the mainstream virtual machines that are still in use. In the IBM model, every virtual machine is a complete copy of a real machine, just a less memory. According to this concept, a powerful large host can be split into a number of virtual machines. These virtual machines are only less resources than the original host.
IBM's virtual machine version is similar to other virtual machines because it is also a service that provides a functional map. This means that the virtual machine is responsible for explaining the virtual instruction and maps them into actual machine instructions. For virtual machines of IBM genre, the mapping of such instructions is basically a one-one mapping. This means that a virtual directive is only corresponding to an actual instruction and completes a practical instruction. In essence, the user is actually an instruction to access and execute the machine.
Now, you may feel very confused: If the IBM VM operating system is actually given all functions of the actual machine, how do it guarantee security? Security is also implemented by mapping. As long as there is a prevented specific instruction set that is considered sensitive, such as those that try to access the processor memory (register). If you are allowed to access such instructions, it is equal to allowing the user to directly modify the actual machine, thereby changing other running virtual machines. If this situation is allowed, then each user's virtual machine is not completely unrelated, and thus the environment of other users can be destroyed.
In essence, IBM VM system performs all non-sensitive instructions directly, while intercepting sensitive instructions. After the machine intercepts these sensitive instructions, it will try to simulate expected operations to enable users to notice they trying to perform illegal operations. If possible, the VM system provides a virtual execution for sensitive instructions, providing users with all their desirable features, while maintaining the system integrity of the OS / 370 hardware. All of these features are provided by virtual operating systems running on hardware.
How did it work?
Therefore, the IBM virtual machine system not only allows shared resources, but also protects system resources.
The virtual machine operating system is the "brain" of the entire IBM virtual machine architecture. The entire system including operating systems and hardware is called virtual machine systems (VM System). Each virtual machine system is controlled by a program called a control program. In addition to managing actual physical hardware, the control program also creates a virtual machine for each system user. This virtual machine is a full simulation of 370 systems or 390 systems. The focus of IBM virtual machine concept is that each user can run programs, store data, and even crash on their virtual machines, which does not affect the virtual machine system itself and other system users. Therefore, the IBM virtual machine model not only allows resource sharing, but also realizes the protection of system resources.
The control program actually runs directly on the host hardware and is the most important part of the virtual machine system. Control Programs To manage system hardware, including system support tasks within booting and shutdown, as well as request queuing and execution. At the same time, the control program also manages programming feature of each virtual machine and the establishment and maintenance of each virtual machine.
An important component of another and virtual machine system user interaction is an important component of the Conversational Monitor System (CMS). This name is a bit complicated, but CMS only provides basic tasks for the operating system required by users. These include file system commands, program load, and execute functions, memory management, screens, and window services, and services that allow users to write applications. CMS is a single user single task operating system. Although the system has the ability to handle multiple tasks at the same time, it is initially used to do a single task system. Each virtual machine has its own CMS copy, so that all users have the same interface and functionality. The IBM virtual machine system instruction set is actually a one-one correspondence
In addition to CMS, there are some other components, including Group Control System, Transpent System Access Facility, Some Additional Services, and Dump Viewing. Facility). I know what you mean by thinking about these official nations. Honestly, those mentioned above are not important to generally understand the IBM virtual machine system. So, we will concentrate on how to discuss how the control procedures and session monitoring systems are mapped.
As mentioned in the review, the instruction set is actually mapped. Based on speed and convenience, most of the instructions on 370 systems and 390 systems are running directly by the system. This means that CMS allows the user to run instructions without speed loss and get the features they want. Now I want to say is a small command subset, and the VM system thinks this instruction subset is sensitive.
A sensitive instructions actually refer to such instructions: it allows users to change the status of another user virtual machine, change the system hardware status, and other sensitive or protected functions. To illustrate this problem, let us look at an example:
For example, a user attempts to perform an instruction that can access other user virtual machines and resources. This instruction will be intercepted by CMS and mark a sensitive instruction. This means that the CMS will regard this instruction as a protected instruction, and then pass this instruction to the control program, add a special sign, this flag will tell the control program: "This is a protected Directive. "Computer terminology is called interrupt, but this is not important for this article.
The control program receives instructions with the flag, tells the control program, which is a sensitive instruction. The control program then performs some specific routines or checks to this instruction to determine how it is handled. These routines can tell whether the program needs to simulate the execution of this instruction, or whether the execution of this instruction is fully prevented. If the control program simulates this instruction, the user will never know that they have just tried to perform a sensitive instruction, and their system will continue to execute as if there is nothing special. If the control program must block the execution of this instruction, then it will return a message to the user telling them an error. The user program is likely to stop execution.
summary
After reading the above paragraph, you have now a basic understanding of what IBM virtual machine model and how IBM virtual machine work. This is very good, but I will bet, do you have to think about this model really work? Is it really like propaganda? I have used this system, honest, it does work.
The IBM virtual machine system provides a way for multi-user sharing large systems in a safe environment.
