Virtual machine
A virtual machine is a piece of computer software designed to reproduce a specific set of computer behaviors and capabilities other than the ones native to the computer or operating system on which the software itself is running.Some virtual machines are emulators; these allow software written for one machine to run on another. Please note that emulation for computer systems can include emulation for both different machine architectures, and operating systems. Others produce behaviors and capabilities of a machine that doesn't necessarily exist as an actual piece of hardware but may only be a detailed specification. For example, the P-code machine specification (one of the first) was a description of a specific set of capabilities and behaviors that programmers could use to write programs that would run on any computer running virtual machine software that correctly implemented the specification. More modern examples include the specification of the Java virtual machine and the Common Language Infrastructure virtual machine at the heart of the Microsoft .NET initiative. These allow diverse computers all to run software written to that specification; the virtual machine software itself must be written separately for each type of computer on which it runs.
Another type of virtual machine lets you run one operating system on top of another on the same machine. One early use of this concept was the IBM CMS operating system. It provided a separate virtual machine environment for each individual user program. In that way, the programs could be written simply as if they were running alone, and the OS quietly provided multitasking and resource management services behind the scenes. This also enabled IBM to upgrade the hardware, install a new version of the CMS VM, and thereby allow user programs to take advantage of the new hardware without being rewritten. The plex86[?] and VMWare[?] packages do the same thing on modern PCs, trapping all hardware accesses and simulating all of a motherboard except for the processor.
A selection of virtual machines:
- Common Language Infrastructure (Microsoft .NET initiative)
- Java virtual machine
- MMIX
- Forth virtual machine
- O-code machine
- P-code machine
- Parrot a virtual machine being developed for Perl 6
- SECD machine
- Smalltalk virtual machine
- Squeak virtual machine
- Warren Abstract Machine
- TrueType virtual machine
- Z-machine
Paret, and spoke of you as one of the coming men.
always surprises me when I think of it, I find it difficult to remember
Have you discovered, too, the emptiness of it all?" she inquired
quizzical glance--"you look quite prosperous and contented, as though you
disagreed with you--you walk into a gallery and see a portrait of--of an
sentimental attachment, and you exclaim that the artist is a discerning
sorry that she ever tried to console herself with baubles it's what
yourself--to be sure of it." And she handed me my tea. "Come now,
regarding me smilingly, with parted lips, "it amuses me a lot--it's.
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