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Some of your questions are because there is a lot of overloaded terminology. Virtual Machine, for example, has two meanings: 1) A system virtual machine provi

Some of your questions are because there is a lot of overloaded terminology. Virtual Machine, for example, has two meanings: 1) A system virtual machine provides a complete system platform which supports the execution of a complete operating system (OS).[1] These usually emulate an existing architecture, and are built with the purpose of either providing a platform to run programs where the real hardware is not available for use (for example, executing on otherwise obsolete platforms), or of having multiple instances of virtual machines leading to more efficient use of computing resources, both in terms of energy consumption and cost effectiveness (known as hardware virtualization, the key to a cloud computing environment), or both. 2) A process virtual machine (also, language virtual machine) is designed to run a single program, which means that it supports a single process. Such virtual machines are usually closely suited to one or more programming languages and built with the purpose of providing program portability and flexibility (amongst other things). An essential characteristic of a virtual machine is that the software running inside is limited to the resources and abstractions provided by the virtual machine—it cannot break out of its virtual environment. The CLI is the second type of virtual machine and something like VirtualBox, VMware, and IBM mainframe VM's are the first kind. > Why byte code? Or, in what sense can each code be only one byte long? Again, it's not "byte code" it's "bytecode" which is defined here: https://en.wikipedia.org/wiki/Bytecode https://en.wikipedia.org/wiki/Bytecode "Bytecode, also known as p-code (portable code), is a form of instruction set designed for efficient execution by a software interpreter"

graycat 11y ago
Thanks. Okay, I know some about the details of IBM's VM and a little about VMware. I have wondered: The way VM has worked on IBM mainframe instruction set has been partly due to an accident of the design of that instruction set and, then, some extensions for VM. Really, that way, tough for the program running to know if it is running as a virtual machine or not. So, in particular, the program running on VM can be using privileged instructions and not know that it doesn't really have access to the real hardware. So I've wondered if the Intel x86 instruction set also has this accident and, thus, can run operating systems that use privileged instructions but not know they are running on a VM. Or maybe the ability to run on a VM was from some extensions to the Intel instruction set. Do you know? Does the Microsoft CLI/CLR software have some security features beyond just any native program in, say, Fortran or assembler running in an address space, process, or whatever Microsoft calls where a program runs? I'm beginning to get the prerequisites for reading the OP, that is, understanding what the long standard alternative to native code has been. Heck, I can understand native code -- at one time I entered some simple programs via the computer console sense switches. And I printed out the object listing from a Fortran compiler and went over the machine language instructions one by one. I discovered that even for some simple code and a good Fortran compiler, assembler could be faster by a factor of several. Just read the Wikipedia article. Nice and easy. Thanks.
- wvenable 11y ago
  > So I've wondered if the Intel x86 instruction set also has this accident and, thus, can run operating systems that use privileged instructions but not know they are running on a VM. Or maybe the ability to run on a VM was from some extensions to the Intel instruction set. Do you know? No, originally x86 was very difficult to emulate in a virtual machine. User-mode can be run directly on the processor but, for kernel-level code, binary translation was necessary to dynamically re-write the code containing privileged instructions. However, these days nearly all modern x86 processors now have extra instructions specifically for virtualization. > Does the Microsoft CLI/CLR software have some security features beyond just any native program There are a bunch of sandboxing features available in the CLR but most applications run with full trust and can do anything a native program can do.
  - graycat 11y ago
    Super! Thanks, I needed that!

graycat 11y ago

Thanks. Okay, I know some about the details of IBM's VM and a little about VMware. I have wondered: The way VM has worked on IBM mainframe instruction set has been partly due to an accident of the design of that instruction set and, then, some extensions for VM. Really, that way, tough for the program running to know if it is running as a virtual machine or not. So, in particular, the program running on VM can be using privileged instructions and not know that it doesn't really have access to the real hardware. So I've wondered if the Intel x86 instruction set also has this accident and, thus, can run operating systems that use privileged instructions but not know they are running on a VM. Or maybe the ability to run on a VM was from some extensions to the Intel instruction set. Do you know? Does the Microsoft CLI/CLR software have some security features beyond just any native program in, say, Fortran or assembler running in an address space, process, or whatever Microsoft calls where a program runs? I'm beginning to get the prerequisites for reading the OP, that is, understanding what the long standard alternative to native code has been. Heck, I can understand native code -- at one time I entered some simple programs via the computer console sense switches. And I printed out the object listing from a Fortran compiler and went over the machine language instructions one by one. I discovered that even for some simple code and a good Fortran compiler, assembler could be faster by a factor of several. Just read the Wikipedia article. Nice and easy. Thanks.

wvenable 11y ago
> So I've wondered if the Intel x86 instruction set also has this accident and, thus, can run operating systems that use privileged instructions but not know they are running on a VM. Or maybe the ability to run on a VM was from some extensions to the Intel instruction set. Do you know? No, originally x86 was very difficult to emulate in a virtual machine. User-mode can be run directly on the processor but, for kernel-level code, binary translation was necessary to dynamically re-write the code containing privileged instructions. However, these days nearly all modern x86 processors now have extra instructions specifically for virtualization. > Does the Microsoft CLI/CLR software have some security features beyond just any native program There are a bunch of sandboxing features available in the CLR but most applications run with full trust and can do anything a native program can do.
- graycat 11y ago
  Super! Thanks, I needed that!