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Interview: Mendel Rosenblum of VMware

by David Sims

VMWare is virtual machine software that lets you run multiple operating systems on a single-processor x86 machine. We talked with VMWare's cofounder and chief scientist, Mendel Rosenblum about VMWare's technology, users, and applications.

Mendel Rosenblum: VMWare is a company that has basically pioneered the idea of running what is referred to as a virtual machine monitor on a commodity PC. And what a virtual machine monitor provides for you is the ability to run multiple operating system environments simultaneously on the PC, so rather than having the limitation which most PCs have now, where you install an OP and that's the one that you boot one at a time and you get to use that. Here, with VMWare, you can actually run as many as you want and basically switch between them as easily as you would switch between processes on a multitasking operating system.

David Sims: How is that handled? Is the virtual machine an application that's running these operating systems?

Rosenblum: Well, we have sort of a unique architecture where we're both an application and what is technically referred to as a virtual machine monitor which is like a special type of operating system. So, when we run one of the additional operating systems you add to your machine, we're actually running in the most privileged mode of the processor and have control of all the hardware on the machine. So, in that sense, you know, we're an operating system that just happens to allow other operating systems to run on top of them. So, we also have a mode in which we run in which we appear to the user as just a normal application running on one of the operating systems. That makes it a lot easier for the user to interact and makes it a lot easier to install and configure us. You download our product on say NT and it installs like using an install shield like any other application. So, the answer is we're kind of both, an application and an operating system.

   Mendel RosenblumMendel Rosenblum, Ph.D.

Chief Scientist, VMWare

• Dr. Rosenblum is an associate professor of computer science at Stanford University.

• He leads the operating systems research group of the FLASH project.

• He is part of the team that developed the the Hive operating system, the SimOS machine simulator and the Disco virtual machine monitor.

• Ph.D. and M.S. in computer science from the UC Berkeley, B.A. in mathematics from University of Virginia.

Sims: I think the analogy that more people have heard of VMWare or would be familiar with would be running PC applications, something like PC soft on the Macintosh.

Rosenblum: Right.

Sims: Is it similar technology?

Rosenblum: Well it appears similar in that you can have it appear like an application that runs a PC application and PC operating system, but the technology is actually very different.

Because we're running on the same like Intel x86 hardware, we can actually directly use the hardware to run the PC software like the operating system applications. And so what our software actually does is actually takes the hardware and uses it to run in these additional operating systems directly. So, unlike the sort of emulation technology like Virtual PC and the stuff that has come up on the Mac, we're not really a simulator and we don't really have the kind of slowdowns you experience when you're running through all these simulation layers, since literally what we're doing is just sort of giving the hardware directly to the operating system and having it run it.

Sims: You know, it's interesting that you mention the slowdown. I have heard that it takes quite a bit of memory to VMWare. Is that your feedback also? How much memory do you recommend on, say a Linux running on a Pentium box?

Rosenblum: Well, I think the minimum memory you would even probably consider doing this is 64 megs and it runs very comfortably in a 128 megs. So we recommend is put as much memory as you can on your machine, but we have people write us all the time saying "I'm running with 64 megs and it's enough." The issue is that, you know, you're running this whole new environment with the applications. It will still run if you don't have the memory, enough physical memory on your machine, it's just that you end up having to go to disk and that can slow you down tremendously. The minimum requirements to actually run the software is even lower than 64 megs it's just that end-user experience, your disk light would be on most of the time, you'd be sitting there waiting for the disk.

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