Choosing between type 1 and type 2 client virtualization

There are two ways to run a virtual machine directly on a client device. Columnist Brian Madden sorts out how they might fit into each enterprise.

One of the trends in the desktop virtualization world is something called "client virtualization," where a virtual machine is run directly on a user's laptop or desktop computer.

This is nice because it's NOT server-based computing, so it works offline and with graphically intense applications. (After all, this "client-based computing" is what's been happening for twenty years!)

When looking at running a virtual machine directly on a client device, there are two types of ways this can be done, commonly called "type 1" and "type 2" solutions. (Seriously, that's all that we could come up with as an industry-at-large!)

Virtualized engine is main OS

In a type 1 client virtualization environment, the virtualization engine is the main "OS" on the client device. In most cases, it's literally installed onto a blank laptop by dropping a DVD into the drive and wiping out the machine. This is commonly called a "client hypervisor" since it runs in a similar way to server hypervisors like VMware ESX or Microsoft Hyper-V.

When one of these client hypervisors is used, every OS is executed as a "guest," and the hypervisor has ultimate control over that hardware.

Type 1 client hypervisors are relatively new, with only two companies (Virtual Computer and Neocleus) shipping products today. Both VMware and Citrix promise to have their own Type 1 client hypervisors by the end of the year.

Virtual app runs on the OS

In a type 2 environment, an OS (like Windows or Mac OS X) is installed like normal on the client. Then a virtualization application is installed on top of the OS, which creates VMs that run "on top" of the existing OS.

(By the way, people often refer to type 2 environments as "type 2 hypervisors," although that's not technically correct since, by definition, a hypervisor is running at the lowest level as in the type 1 scenario. Type 2 scenarios should really be called "type 2 virtualization environments" or "type 2 platforms" or something. They should definitively NOT be called "hypervisors."

Examples of type 2 virtualization environments include VMware Fusion and VMware Workstation, Microsoft Virtual PC, Parallels Workstation, and Virtual Box.

Choosing between type 1 and type 2

In many ways, type 1 and type 2 environments are similar: they both allow complete virtual machines run locally on a client device while separate from a locally-installed OS. And that's the key here. With client virtualization, an administrator can completely build, configure, secure, and deploy a complete "corporate" VM that runs locally on an end user's client device.

In case you're wondering about the practical differences between type 1 and type 2 client virtualization environments, think of it like this: Since Type 1 environments replace the local OS, they're most often used when the corporation owns the client asset and when the virtual client is the primary OS the user uses.

Type 2 environments, conversely, make the most sense in situations where the user owns their own device or where they only occasionally run applications from their VM.

Brian Madden, Independent Industry Analyst and Blogger
Brian Madden is known throughout the world as an opinionated, super technical, fiercely independent desktop virtualization expert. He's written several books and over 1,000 articles about desktop and application virtualization. Brian's blog,, receives millions of visitors per year and is a leading source for conversation, debate and discourse about the application and desktop virtualization industry. Brian is also the creator of BriForum, the premier independent application delivery technical conference.

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