Virtual machine - Revision history

Jnc: Give an example of a machine which cannot be virtualized

2024-10-28T12:46:57Z

Give an example of a machine which cannot be virtualized

Jnc: /* See also */ +CP operating system

2023-01-05T17:19:57Z

‎See also: +CP operating system

Jnc: +cat

2018-12-16T21:17:28Z

+cat

Jnc: Mention hypervisor, clarify needed support

2018-11-01T12:55:18Z

Mention hypervisor, clarify needed support

Jnc: punc

2017-10-18T18:59:55Z

punc

Jnc: A decent start

2017-09-23T22:20:28Z

A decent start

New page

A '''virtual machine''', or '''virtualization''', refers to a technique in with the [[operating system]] on a particular machine, in cooperation with the machines [[Central Processing Unit|CPU]], provides to the [[process]]es running on it the illusion that they are alone on a bare machine.

Operating systems which provide the capability are called 'virtual machine' (VM) OSs; if the VM OS is properly designed and implemented, it is usually possible to run another copy of the VM OS inside a process running in the same VM OS, but on the 'bare' hardware. This capability can be useful for testing new versions of the VM OS, etc.

Not all computers can be virtualized; it requires that the machine hardware be carefully designed so that any and all operations which could disrupt the overall operation of the machine (e.g. resetting all the I/O devices) can be preventing from happening, but instead result in a [[trap]] to the OS, so that it may simulate that action.

Some actions, such as device I/O, are simulated in a restricted way; e.g. attempts to read and write [[disk]]s may instead result in reads and writes to a file which has been configured (at the time the virtual machine was started) to represent the disk(s) attached to that virtual machine.

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 Not all computers can be virtualized; it requires that the machine hardware be carefully designed so that any and all operations which are reserved to the operating system are not only preventing from happening when a [[user]] tries to perform them, but instead result in a [[trap]] to the OS, so that it may simulate that action.
-Some machines merely ignore operations which could disrupt the overall operation of the machine (e.g. resetting all the I/O devices) when a user tries them, making it impossible for the operating system to simulate them for virtualization purposes.
+Some machines (such as the [[PDP-11]]) merely ignore operations which could disrupt the overall operation of the machine (e.g. resetting all the I/O devices) when a user tries them, making it impossible for the operating system to simulate them for virtualization purposes.
 Some actions, such as device I/O, are simulated in a restricted way; e.g. attempts to read and write [[disk]]s may instead result in reads and writes to a file which has been configured (at the time the virtual machine was started) to represent the disk(s) attached to that virtual machine.

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		+	==See also==
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		+	* [[CP operating system]]

	[[Category: OS Basics]]		[[Category: OS Basics]]

← Older revision		Revision as of 21:17, 16 December 2018
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		+	[[Category: OS Basics]]

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-A '''virtual machine''', or '''virtualization''', refers to a technique in with the [[operating system]] on a particular machine, in cooperation with the machine's [[Central Processing Unit|CPU]], provides to the [[process]]es running on it the illusion that they are alone on a bare machine.
+A '''virtual machine''', or '''virtualization''', refers to a technique in which [[hypervisor]] [[software]] on a particular machine, in cooperation with the machine's [[Central Processing Unit|CPU]], provides to the [[process]]es running on it the illusion that they are alone on a bare machine.
-Operating systems which provide the capability are called 'virtual machine' (VM) OSs; if the VM OS is properly designed and implemented, it is usually possible to run another copy of the VM OS inside a process running in the same VM OS, but on the 'bare' hardware. This capability can be useful for testing new versions of the VM OS, etc.
+[[Operating system]]s which provide the capability are called 'virtual machine' (VM) OSs; if the VM OS is properly designed and implemented, it is usually possible to run another copy of the VM OS inside a process running in the same VM OS, but with the latter on the 'bare' hardware. This capability can be useful for testing new versions of the VM OS, etc.
-Not all computers can be virtualized; it requires that the machine hardware be carefully designed so that any and all operations which could disrupt the overall operation of the machine (e.g. resetting all the I/O devices) can be preventing from happening, but instead result in a [[trap]] to the OS, so that it may simulate that action.
+Not all computers can be virtualized; it requires that the machine hardware be carefully designed so that any and all operations which are reserved to the operating system are not only preventing from happening when a [[user]] tries to perform them, but instead result in a [[trap]] to the OS, so that it may simulate that action.
 Some actions, such as device I/O, are simulated in a restricted way; e.g. attempts to read and write [[disk]]s may instead result in reads and writes to a file which has been configured (at the time the virtual machine was started) to represent the disk(s) attached to that virtual machine.

← Older revision		Revision as of 18:59, 18 October 2017
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−	A '''virtual machine''', or '''virtualization''', refers to a technique in with the [[operating system]] on a particular machine, in cooperation with the ~~machines~~ [[Central Processing Unit\|CPU]], provides to the [[process]]es running on it the illusion that they are alone on a bare machine.	+	A '''virtual machine''', or '''virtualization''', refers to a technique in with the [[operating system]] on a particular machine, in cooperation with the machine's [[Central Processing Unit\|CPU]], provides to the [[process]]es running on it the illusion that they are alone on a bare machine.

	Operating systems which provide the capability are called 'virtual machine' (VM) OSs; if the VM OS is properly designed and implemented, it is usually possible to run another copy of the VM OS inside a process running in the same VM OS, but on the 'bare' hardware. This capability can be useful for testing new versions of the VM OS, etc.		Operating systems which provide the capability are called 'virtual machine' (VM) OSs; if the VM OS is properly designed and implemented, it is usually possible to run another copy of the VM OS inside a process running in the same VM OS, but on the 'bare' hardware. This capability can be useful for testing new versions of the VM OS, etc.