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An Introduction to Virtualization
An Introduction to Virtualization
Date: October 28th, 2008
Topic: IT Computing
Manufacturer: Various
Author: Liz van Dijk
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Introduction

Over the course of the past couple of months, the AnandTech IT team has been putting a lot of time into mapping out and clarifying the inner workings of several interesting forms of virtualization. The purpose of these articles was not primarily to cover "news" (however current the topic might be), but to create a sort of knowledge base on this subject at AnandTech, as we find many people interested in learning more about virtualization are met with a large amount of misinformation. Secondly, we believe a better knowledge on the subject will empower the people in control of their company's IT infrastructure and help them make the correct decisions for the job.

There's no denying that virtualization is changing company's server rooms all over the world. It is promoting both innovation and the preservation of aged applications that would otherwise not survive a migration to modern hardware platforms. Virtualization is completely redefining the rules of what can and cannot be done in a server environment, adding a versatility to it that is increasing with every new release. We believe that when making big changes to any existing system, the more information that is available to the people given that task, the better.

But what about desktop users?

While the above should make it clear why businesses are extremely interested in this technology, and why we have been digging so deep into its inner workings, we are also noticing an increased interest from the rest of our reader base, and have been flooded with questions about the how and why of all these different kinds of virtualization. Since we don't want to leave any interested people out in the cold, and the in-depth articles may seem a bit daunting to anyone looking to get an introduction, here is another article in our "virtualization series". In it, we will attempt to guide our readers through the different technologies and their actual uses, along with some interesting tidbits for regular desktop users.

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16 Comments - Last by steveyballme, 369 days ago
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WINE Vs. OS Virtualization by murphyslabrat, 388 days ago
You seemed to have addressed the issue in the end, but my question is: as far as PC Gaming goes, is there any reason to use a virtual machine. If the answer is yes, then which approach is typically best, and what would be the recommendation for software.

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RE: WINE Vs. OS Virtualization by Denithor, 388 days ago
Read page 11 of the article.

Yes, in certain cases. If you're running OS X or Linux you can run a virtual copy of XP which can then run a game not supported by your "true" operating system. However, it's going to add overhead, therefore reducing performance (game speaks to the virtual XP which has to speak to the real OS which talks to the hardware). Newer games probably won't work very well because they need as much hardware as they can get so the extra baggage will just weigh them down.

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Classic gaming by MontagGG, 388 days ago
You should be able to run a virtual Win98 in Vista to play classic games. This does require the premium editions.

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A practical comparison would be nice by FATCamaro, 388 days ago
I wasn't clear on how the different hypervisor products compared (ESX, Xen, MS?) with respect to binary translation or paravirtualization without looking at your other article. A summary here would have been nice.

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No info on AMD-V, VT-x or VT-d? by Vidmo, 388 days ago
I was hoping this article would get into some of the latest hardware technologies designed for better virtualization. It's still quite confusing trying to determine which hardware platforms and CPUs support VT-d for example.

The article is a nice software overview, but seems incomplete without getting into the hardware side of the issues.


Reply
RE: No info on AMD-V, VT-x or VT-d? by LizVD, 388 days ago
Thanks for the input!

The real purpose of this article was to provide a "beginner-safe" intro into the things we have been discussing on Anandtech IT for the past couple of months, so in-depth discussion of each of the technologies is something we avoided on purpose, to keep focus on the basic differences without getting carried away.

Your question is an interesting one, however, and of the sort we'd like to properly address in our blogs, so keep an eye on them, as we'll be looking into it.

Reply
RE: No info on AMD-V, VT-x or VT-d? by Vidmo, 388 days ago
Ahh I somehow missed the link to your hardware article.
http://it.anandtech.com/IT/showdoc.aspx?i=3263&p=1

Very well done. Would it be possible to update that article to reflect VT-d and possibly TV-i technologies as well?

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RE: No info on AMD-V, VT-x or VT-d? by solusstultus, 388 days ago
Hardware support for VT is not used by most/any? commercial hypervisors (VMware doesn't use it) and has been shown to actually have lower performance in many cases than binary translation:

http://www.vmware.com/pdf/asplos235_adams.pdf

Reply
RE: No info on AMD-V, VT-x or VT-d? by duploxxx, 388 days ago
unfortunately your link is 2 years old.

Current statement for Vmware ESX is that you should use the hardware virtualization layer when you have 64bit OS at any time and when virtualization layer 2 aka NPT from amd (ept when intel launches nehalem next year) at any time.

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RE: No info on AMD-V, VT-x or VT-d? by solusstultus, 387 days ago
While I don't claim to be an expert, that's the most recent study that I have seen that actually lists performance results from both techniques.

If you have seen more recent results, do you have a link? I would be interested in reading it.

From what I have seen, NPT addresses overheads associated with switching from the Guest to the VMM during page table updates (which can occur frequently when using small pages). However, the other main source of overhead cited in the paper that I referenced were traps into the VMMs on system calls which could be replaced by less expensive direct links to VMM routines in translated code. So unless the newer hardware support virtualization implementations address this (they might, I haven't looked at the documentation), it seems translation could still be potentially faster for some apps, and that an ideal implementation would make use of both in different situations.

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