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Step 2: Know the Virtual PC Interfaces

This article will have us blitzing through many, many settings, so you need to understand 1) the visual cues; 2) the Virtual PC Preferences; and 3) the PC settings you can make for each virtual instance.

Visual Cues

Virtual PC does a good job of showing us how well each virtual instance is running, in real time. Does this require loading another, separate application, one that sucks up precious processing power? No, the indicators are as plain as the nose on your face. Figure 1 shows the performance readout that appears at the bottom of every Virtual PC instance screen.

Figure 1

Figure 1 Visual cues.

Table 1 describes each icon and the information it displays. If you click each icon and hold down the mouse button, a menu appears that allows you to shortcut to configuration options. We'll concentrate on those icons that impact performance most, and briefly cover the shortcuts provided.

Table 1 Virtual Machine Performance Cues


Performance Impact

Shortcut Interface to...

Disk activity

This icon appears during disk access. If performance seems slow and there are a lot of flashes here, the application is going to disk too much, which is often a sign of memory starvation. Increase allotted memory.

The settings to each virtual drive and to the Virtual Disk Assistant.

CD-ROM activity

This icon shows CD-ROM accesses. Expecting CD-ROM access but seeing none? This is a clue that you need to check the CD-ROM's mount status, especially when running a UNIX system without automounter. Before you can use a CD, you must have Virtual PC "capture" it.

Mounted CD-ROM's titles and to the eject functionality. You can also capture a CD-ROM to use it temporarily or capture the CD-ROM disc image and store it to your virtual hard disk.

Shared Folder activity

Shared folders allow you to access volumes on the host iBook or Macintosh. This allows you to access data without storing a copy on the virtual disk itself.

Shared folder settings, including active shared folders. Use this shortcut to enable the PC to access the host machine's local and network drives. Shared folders work exclusively with Windows systems.

Network activity

This icon shows network activity. You should see a few flashes during virtual machine startup. If not, this is a sign that the operating system cannot recognize the virtual network adapter. If you see more flashes than expected for your task, look into background tasks hogging the network: spyware, automatic patch downloads, retransmissions, etc. Network activity takes a lot of processing power.

Network settings and virtual switch settings.

USB activity

Got a USB device that has cross-platform support—for example, a printer or iPod configured to offer USB storage? Plug it in and play! Simultaneous read/write access to a file across several operating systems, each with their own unique and conflicting file lock mechanisms, is not possible. You cannot share a USB device across instances.

USB settings, used to select which USB devices are used exclusively by the Virtual PC instance. There is a way to access a USB device through the host, when it's a shared folder.

Printer activity

Plug in a printer, and if the virtual instance operating system has a driver for it, you can watch the activity here. If you have no activity, make sure that the driver is working as expected.

Printer settings and setup.

CPU/processor activity

This icon is the heart of your performance efforts. Next to the central processing unit (CPU) icon are four load bars that show CPU load. Have performance problems and four lit bars that stay at peak processor load? That's a sign that something is wrong. This article will show you how to trim the processor load from the baseline settings and from XP itself.

CPU Usage preferences.

This is a lot of information, but with it you can visually determine basic issues that hurt performance. You can use these clues to focus your troubleshooting. Now let's explore Virtual PC settings a little more.

Virtual PC Preferences

Virtual PC baseline preferences must be chosen carefully. Each setting is applied to all instances. Want to ensure that the XP instance you run is very responsive? Want to give it more processing power when it's put into the background? When you configure high background processing, every instance gets that star treatment, which in turn will lower the number of instances your machine can support.

Figure 2 illustrates the basic baseline Virtual PC preferences. The interface is laid out nicely. The table on the left half of the dialog box shows the preference and the right half shows the current state of that preference:

Figure 2

Figure 2 Virtual PC baseline settings.

Table 2 reviews these settings, focusing on those baselines with performance impacts.

Table 2 Virtual PC Preferences


Performance Impact

PC Behavior

Pauses virtual instance processing when the virtual instance application is no longer in focus. This preference affects all Virtual PCs. Some host systems may not support several instances fighting for processing power while they're minimized or running in the background.

Virtual Switch

Controls how networking is implemented. Virtual instances can get networking through shared networking or through the virtual switch. Shared networking is implemented very much like the Internet sharing in the System preferences. With this configuration, all traffic "routes through" the host operating system and is visible to it. The other option, virtual switch, allows the virtual machine to bind to the network interface directly, much like the host operating system. This preference designates an interface for the virtual switch. For example, my iBook has a built-in Ethernet and AirPort interface. This setting allows me to choose which interface the virtual machines bind to when they use the virtual switch.


Playing MP3 music in the background can really consume processor power. Try playing your music on the host machine versus in a virtual instance.

CPU Usage

By default, virtual machines pause when they lose focus. This preference allows you to enable and to adjust background activity. The more activity you allow with this preference, the less is available to any instance, host or virtual, running in the foreground. If you're running complex calculations in the foreground, you may want to drop the amount of processing allowed in the background.

This preference can also enable automatic restart of all running PCs at Virtual PC start up. Imagine starting 10 applications on your Mac at system startup!


Controls which icons appear at the bottom of the window. Remember, each icon not only shows performance information; it's a shortcut to settings.


Determines whether Virtual PC loads at startup. You may find this setting useful, or a waste of processor power. This decision only loads the controller software; it doesn't load any specific instance by default. That's controlled by the CPU Usage preference.

Performance tuning begins by determining just what baseline preferences you want to enable for all virtual PCs. Enable too much background processing and you'll limit the number of instances a great deal, depending on your mix of applications and processing needs. Now that you have your basic architecture planned, let's consider the settings made on each Virtual PC.

Virtual Instance/PC Settings

Okay, right now you know how to interpret the visual clues that the Virtual PC icons provide. You know the basic baseline settings for all Virtual PC machines and how the preferences affect performance. Let's review the settings you can make on each PC (see Figure 3).

Figure 3

Figure 3 PC settings.

Table 3 reviews some of these settings and how they affect performance.

Table 3 PC Settings and Performance Impact

PC Setting

Performance Impact

PC Memory

Determines how much memory is dedicated to the PC. The same panel will let you determine how much is dedicated for video. Once the PC is started, this setting cannot be changed without requiring a reboot. Trial-and-error is the best way to get the best performance. Some operating systems take more RAM than others, and the same is true for applications.

Drive 1, Drive 2, Drive 3

Assigns virtual disks to a PC. I built my XP system with too little space, it turns out. It was a fixed disk and couldn't be expanded, so I created a second disk and assigned it. Sometimes having separate disks for the operating system and for key applications can help performance.

Shared Folders

Shares data across the PCs and the host system without needing to create multiple copies. Enabling this setting will create SMB shares that allow you to access the Mac hard drive as drive Z:. You can automagically share the local volumes, network volumes, and removable media with this setting. This allows you to share USB devices such as iPods across multiple PCs and the host machine, something that isn't possible normally.

Shared folders capability is installed by mounting a virtual Additions CD. This software, created for OS/2, DOS, and Windows systems (not Linux), has the shared software code. To share files among the PCs, you must implement a manually produced NFS or Samba solution.


If you don't need networking for a PC, disabling it helps performance. Disabling networking is as simple as unchecking a check box. From here, you can configure the network to use the virtual switch or shared networking.


If you aren't using the USB port for a PC, disable it and prevent needless port polling for a connection.

Finally! You now have an understanding of all those basic settings and how they affect performance on both a global basis (Virtual PC baseline settings) and a local basis (PC settings). Let's use all this information to tune an XP system for better performance.

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