What virtualization is -- and what it isn't

When a computer or an operating system uses software to do anything it normally can't, the enabling technology tends to get labeled "virtualization." Well, don't believe everything you read (except here). Let's see what virtualization is and is not.

System virtualization rescinds operating systems' right to own, or refusal to share, property -- hardware resources including memory, CPU cycles, allocated units of storage, I/O ports, and even the display, mouse, and keyboard. Operating systems expect exclusive ownership of system hardware, a lamentable remnant of such dinosaur OSes as CP/M and MS-DOS.

True system virtualization, exemplified by the familiar Microsoft and VMware products, pries the OS's hands loose from system hardware by constructing one or more convincing mirages of a complete computer system. Guest operating systems are tricked into thinking they have an entire computer to themselves. Storage virtualization manages and aggregates remote storage while mimicking a native direct interface (for example, SCSI) that gives OSes the comfort of owning a resource they shouldn't. Storage virtualization can be done in hardware or software and does not require system virtualization. System virtualization can also be managed in hardware, but this capability is only now coming to the PC and in a relatively primitive form.

Now let's consider technologies that are not virtualization. If misleading terminology were a crime, Microsoft's Virtual PC for Mac would deserve the death penalty. The product had the misapplied moniker when Microsoft acquired its maker, but the fact that it looks and acts exactly like the proper desktop virtualization software Microsoft sells as Virtual PC gives virtualization a black eye it doesn't deserve. Virtual PC for Mac is actually an emulator: It creates a very slow x86 CPU in software on a PowerPC-based system, then emulates a very slow x86-based personal computer. Of course, true virtualization also imposes overhead -- in my experience, depending on the product, 25 to 40 percent. Yet Virtual PC 7.0.2 running on a Power Mac Quad running four 2GHz PowerPC cores has Windows XP reporting that it's running on a 533 MHz x86. You do the math. Clearly, emulation is not virtualization.

Apple's Rosetta, a standard facility of OS X for Intel-based Macs, takes another non-virtualization technology that, on its face, has the disadvantages of Virtual PC for Mac. Rosetta takes OS X applications compiled for PowerPC processors and runs them on x86-based Macs. It distinguishes itself in that it only needs to translate PowerPC machine instructions to x86. Everything else is real; there's no need to emulate the computer or run everything through multiple layers of software. When an OS X for PowerPC application makes a resource request while it's running in Rosetta, after translation from PowerPC to x86 the request is made directly to OS X. As a result, Rosetta doesn't need to fire up an additional instance of OS X. A Mac application, even one built from open source, doesn't know or need to care that its CPU is a mirage.

Emulation and instruction translation are valid solutions to problems that system virtualization can't address -- namely, crossing architectural boundaries. But their performance, resource requirements, and feature limitations generally render them inadequate for day-to-day operation. One the other hand, virtualization is safe, adaptable, and getting faster. That's what you need.

Join the newsletter!

Error: Please check your email address.
Rocket to Success - Your 10 Tips for Smarter ERP System Selection
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Tom Yager

Show Comments



Victorinox Werks Professional Executive 17 Laptop Case

Learn more >



Back To Business Guide

Click for more ›

Brand Post

Most Popular Reviews

Latest Articles


PCW Evaluation Team

Andrew Teoh

Brother MFC-L9570CDW Multifunction Printer

Touch screen visibility and operation was great and easy to navigate. Each menu and sub-menu was in an understandable order and category

Louise Coady

Brother MFC-L9570CDW Multifunction Printer

The printer was convenient, produced clear and vibrant images and was very easy to use

Edwina Hargreaves

WD My Cloud Home

I would recommend this device for families and small businesses who want one safe place to store all their important digital content and a way to easily share it with friends, family, business partners, or customers.

Walid Mikhael

Brother QL-820NWB Professional Label Printer

It’s easy to set up, it’s compact and quiet when printing and to top if off, the print quality is excellent. This is hands down the best printer I’ve used for printing labels.

Ben Ramsden

Sharp PN-40TC1 Huddle Board

Brainstorming, innovation, problem solving, and negotiation have all become much more productive and valuable if people can easily collaborate in real time with minimal friction.

Sarah Ieroianni

Brother QL-820NWB Professional Label Printer

The print quality also does not disappoint, it’s clear, bold, doesn’t smudge and the text is perfectly sized.

Featured Content

Product Launch Showcase

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?