Introduction to Virtual Machines (v)--IBM virtual machine model

IBM Virtual Machine Model



In the IBM model, each virtual machine is a full copy of the real machine, but with little memory.



The IBM (International Business machines) version of the virtual machine is one of the mainstream virtual machines that are still in use. In the IBM model, each virtual machine is a full copy of a real machine, but with little memory. According to this concept, a powerful mainframe can be split into many virtual machines. These virtual machines only have a little less resources than the original hosts.



IBM's virtual machine version is similar to other virtual machine genres because it is also a service that provides feature mapping. This means that the virtual machines are responsible for interpreting virtual instructions and mapping them to actual machine instructions. For IBM-Genre virtual machines, the mapping of this instruction is basically a mapping. This means that a virtual instruction corresponds only to an actual instruction and completes the work of a practical instruction. Essentially, the user is actually accessing and executing the machine's instructions.



Now, you may be wondering: If the IBM VM operating system is actually giving users all the functionality of the actual machine, how does it guarantee security? Security is also achieved through mapping. It is only possible to block or restrict a particular set of instructions that is considered sensitive, such as those that attempt to access the processor's memory (registers). Allowing access to such instructions is tantamount to allowing the user to modify the actual machine directly, thereby altering other running virtual machines. If this is allowed to happen, then each user's virtual machine is not completely irrelevant, and may thus compromise the environment of other users.



Essentially, the IBM VM system executes all insensitive instructions directly, while intercepting sensitive instructions. When the machine intercepts these sensitive instructions, it tries to simulate the expected operation so that the user will not be aware that they are trying to do an illegal operation. If possible, VM systems provide a virtual execution for sensitive directives to provide users with all the functionality they want, while maintaining the system integrity of the os/370 hardware. All of these features are provided by the virtual operating system running on the hardware.



How does it work?







Therefore, the IBM virtual machine system not only allows sharing of 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 the operating system and hardware, is called the Virtual machine system (VM systems). Each virtual machine system is programmed with a program called a control program. In addition to managing the actual physical hardware, the control program creates a virtual machine for each system user, which is a 370-system or 390-system full-true simulation. The IBM virtual machine concept focuses on the fact that each user can run programs on their virtual machines, store data, and even crash the virtual machine, 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 enables 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. The control program manages system hardware, including system support tasks such as startup and shutdown, and requests queued and executed. At the same time, the control program also manages the programming characteristics of each virtual machine and the establishment and maintenance of each virtual machine.



In addition to the control program, another important component of interacting with virtual machine system users is the session monitoring system (conversational monitor system,cms). This name sounds a bit complicated, but the CMS only provides basic tasks for the operating system that the user needs. These include file system commands, program loading and execution functions, memory management, screen 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 was initially used as a single task system. Each virtual machine has its own CMS copy, allowing all users to have the same interface and functionality.



The instruction set of the IBM virtual machine system is actually a one-to-one



In addition to CMS, there are other components of the VM system, including group control systems, transparent system access tools (transparent system access facility), some additional services, And the Dumping View tool (dump viewing facility). I know you're probably thinking about what all these wordy official nouns mean. To be honest, the things mentioned above are not important for a general understanding of IBM Virtual Machine systems. So we're going to focus on how the program and the session monitor system map the instructions.



As mentioned in the review, the instruction set is actually one by one mapped. Based on the considerations of speed and convenience, most of the instructions on the 370 system and 390 systems are run directly by the system. This means that the CMS allows users to run instructions without losing speed and get the functionality they want. Now what I want to say is a small subset of instructions that the VM system considers to be sensitive.



A sensitive instruction actually refers to a directive that allows the user to change the state of another user's virtual machine, change the system's hardware state, and other sensitive or protected functions. To illustrate this issue, let's look at an example:



For example, a user tries to execute a command that accesses other users ' virtual machines and resources. This instruction will be intercepted by CMS and marked as sensitive instructions. This means that the CMS will take this instruction as a protected instruction and then add a special flag to the control when it is passed to the control program: "This is a protected instruction." "Computer terminology is called interruption, but it's not important for this article."



The control program receives a marked instruction, which tells the control program that this is a sensitive instruction. The program then executes some specific routines or checks on the instruction to determine how to handle it. These routines can tell the control program whether it needs to simulate the execution of this instruction, or whether it will completely block the execution of this instruction. If the control program simulates this instruction, the user will never know that they are just trying to execute a sensitive instruction, and their system will continue to execute as if nothing special happened. If the control program must prevent execution of this instruction, it will return a message to the user telling them that an error has occurred. It is likely that the user program will stop execution.



Summary



After reading these paragraphs, you now have a basic understanding of what the IBM virtual machine model is and how IBM virtual machines work. It's good, but I bet you're wondering if this model really works? Does it really work as advertised? I have used this system, and to be honest, it does work.



IBM Virtual Machine system provides a way for multi-user to share large systems in a secure environment.



The IBM virtual machine system provides a way to share large systems in a secure environment with multiple users. By creating a copy of the real machine for each user, the IBM system allows each user to obtain the same functionality and resources without compromising the encapsulation and security of any user. After nearly 30 years of development, the system has been sufficiently stable. This makes it widely used as a resource sharing system in enterprises and universities.