Microsoft® Virtual PC 2004 Technical Overview

By Jerry Honeycutt

Published November 2003

Abstract

Microsoft® Virtual PC 2004 allows users to conveniently run multiple operating systems on a single computer. Users can switch operating systems as easily as they switch applications—instantly, with a mouse click. As a migration tool, Virtual PC provides a cost-effective safety net for certain employees to run critical legacy applications on an interim basis while you continue migrating to a new operating system. Virtual PC also helps companies more rapidly develop, test, support, and deploy applications. This document presents a technical overview of Virtual PC and how it can benefit your company.

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Contents

Acknowledgments              3

Virtual PC Overview              4

Virtual PC Features              7

PC Virtualization              8

Virtual Hard Disks              9

Networking              10

Virtual Machine Additions              12

Virtual PC Requirements              13

Virtual PC in Action              15

Installation              15

Configuration              15

Guest Operating Systems              17

Guest Applications              19

Virtual PC Scenarios              20

Legacy Support              20

Technical Support              21

Quality Assurance              22

Training              23

Migration Testing              23

Summary              26

For More Information              27

Acknowledgments

Bryan Chee, Microsoft Corporation

Kurt Schmucker, Microsoft Corporation

Carla Huffman, Microsoft Corporation

Robert Larson, Microsoft Corporation

Ben Armstrong, Microsoft Corporation

Elsa Rosenberg, Studio B Productions

David Talbott, Studio B Productions

Virtual PC Overview

Microsoft® Virtual PC 2004 is software that lets users run two or more x86 operating systems on their computers—concurrently. It prevents complicated multi-boot configurations in environments where people must use multiple operating systems (whether because of incompatible legacy applications or as a safeguard during migration). Users install multiple guest operating systems in virtual machines. Figure 1 shows Microsoft Windows® XP Professional with two virtual machines open: Windows NT® Workstation 4.0 and Windows 98. Virtual PC emulates a physical computer so exactly that the applications users install in them don’t distinguish the virtual machine from a physical computer. Instead of installing operating systems on multiple, costly computers or creating unwieldy multi-boot installations, you can install the operating systems in multiple, inexpensive virtual machines. Changes that users make in virtual machines don’t affect their physical computers. Virtual PC makes using multiple operating systems easier.

Figure 1. Windows NT Workstation 4.0 and Windows 98 Guest Operating Systems in Windows XP

Virtual PC is a time and cost-saving solution in any scenario in which users must run multiple operating systems. In the enterprise, it provides you a low-cost safeguard for maintaining legacy applications during migration. And it allows employees to run mission-critical legacy applications temporarily while you continue migrating to a new operating system, such as Windows XP. The result is you don’t have to delay a cost-saving deployment until your company can replace or update mission-critical legacy software. You also don’t need to purchase additional equipment just to support legacy software that doesn’t run on the corporate-standard version of Windows. Instead, you can deploy Windows XP with Virtual PC to allow users who must run applications that are incompatible with Windows XP. Then, they can install a compatible version of Windows or OS/2 in a virtual machine and run the legacy application in that virtual machine. Once the operating-system migration is complete and the legacy applications are updated, you can remove Virtual PC from those computers and install the applications in Windows XP.

Other scenarios in which people typically use multiple operating systems include technical support, quality assurance, and training. In the case of technical support, Virtual PC helps support technicians provide quicker responses and reduce call times. Rather than maintaining multiple computers or restarting computers for different support calls, they can simply start a pre-built virtual machine that matches the caller’s configuration—almost instantly. With Virtual PC, test engineers are able to test applications against a wider variety of configurations in shorter amounts of time. Virtual PC provides quicker turnaround times for training rooms and enables more diverse classes based on more configurations. Table 1 summarizes the benefits, and the section “Virtual PC Scenarios” provides more information about how Virtual PC benefits all of these scenarios.

Table 1. Virtual PC Benefits

Virtual PC Features

The benefits of using Virtual PC include the following:

·         Configurability. Users can configure virtual machines, add or remove memory, and install or uninstall applications. Users can create a variety of environments, and Virtual PC is so easy to use and configure that most users require no training at all. Also, the product lets you control the configuration of Virtual PC in locked-down environments.

·         Easy installation. Virtual PC gives users two options for adding new guest operating systems. First, they can install a guest operating system manually. This is almost identical to installing the operating system on a physical computer. In migration scenarios, you’ll probably build configurations in advance and then deploy them to users.

·         Standardization. Since the virtual machine hardware does not change between physical computers, using one physical computer, you can configure and test upgrades and installations on virtual machines, and then you can deploy throughout your company a standard configuration that avoids bugs caused by minor differences between hardware platforms. This approach eliminates exhaustive testing on computer after computer.

·         Convenience. Users switch between operating systems as easily as they switch between applications. They simply click the window containing the virtual machine. They can pause individual virtual machines so they stop using CPU cycles on the physical computer. They can also save virtual machines to disk and restore them at a later time. The restoration process normally takes a few seconds—much faster than restarting the guest operating system. Users manage running, paused, and saved virtual machines through a single, convenient user interface.

·         Host integration. Integration makes interoperability between the guest and host operating systems easy. For example, users can copy, paste, drag, and drop between guest and host. Virtual PC provides Virtual Machine Additions that you install in a guest operating system to enable this functionality.

Each virtual machine acts like a standalone computer. It has its own sound, video, hard disk and network cards and its own processor. And each virtual machine runs its own operating system. Users can install and run most x86 operating systems in a virtual machine.  Microsoft fully supports the following operating systems running in a virtual machine on Virtual PC: Windows 95, Windows 98, Windows Me, Windows NT 4.0 Workstation, Windows 2000 Professional, Windows XP, MS-DOS®, OS/2 Warp Version 4 Fix Pack 15, OS/2 Warp Convenience Pack 1, and OS/2 Warp Convenience Pack 2. Users can also install Windows Server operating systems and numerous third-party operating systems, including Red Hat Linux, Novell NetWare, and others.  Any application that users install in their virtual machines work normally, including business, education, entertainment, Internet, and other programs. And devices that users connect to their physical computers, such as printers, modems, CD-ROM drives, and so on, work normally in their virtual machines. Standard USB input devices such as keyboards and mice are supported through PS/2 emulation, but Virtual PC does not support USB devices that require their own drivers.  Virtual machines also don’t see the physical computer’s hardware video card as a native device, so you can't install your own video card drivers. In addition, SCSI devices are not supported in a virtual machine.

The following sections provide an overview of the technologies in Virtual PC. The section “PC Virtualization” describes how Virtual PC virtualizes computers. The section “Virtual Hard Disks” describes the types of virtual hard disks that Virtual PC provides. And the section “Networking” describes the different networking modes that are available in a virtual machine.

PC Virtualization

Normally, computers run one operating system at a time. As Figure 2 shows, applications run on top of the operating system. The operating system uses device drivers to address the computer’s hardware. And the hardware includes the mouse and keyboard, processor, memory, disk drives and drive controllers, video cards, network cards, and other physical devices. In other words, a computer contains one set of devices, runs one operating system at a time, and has one set of applications on that operating system.

Figure 2. Physical Computers

On the other hand, Virtual PC uses virtual machine technology to run two or more operating systems and their related applications at the same time, as Figure 3 shows. In fact, only the physical computer’s resources, such as memory and disk space, limit the number and variety of operating systems and programs that users can run. The more memory that’s available, the more operating systems the user can run at the same time.

As shown in the figure, guest operating environments rely partially on emulated hardware and partially on virtualized hardware. Virtual PC emulates many of the virtual machine’s hardware in software. Emulated hardware components include the interrupt controller, DMA controller, IDE/ATA controller, non-volatile RAM, real-time clock, buses, I/O controller, keyboard controller, memory controller, programmable timers, and power-management hardware. Virtual PC then uses the host operating system to interact with any external devices – like the CD-ROM, floppy, keyboard, mouse or physical display.

Figure 3. Virtual Machines

Virtual Hard Disks

Virtual PC supports virtual hard disks in a number of powerful and flexible ways. Users can associate several virtual hard ...