Virtual Machine (VM) technology provides great flexibility, but at the cost of raw performance. New chips might help improve VM performance in the future, but until then, use these tips to optimize the performance of both your Microsoft and VMware VM products.

10. Install the tools—Install the collection of tools that comes with your VM product; they improve the guest OS's video performance and mouse responsiveness by providing an optimized SVGA video driver.

9. Provide adequate free disk space—Each VM requires from 4GB to 50GB—or more—of storage. Even if you have the necessary storage, performance can be severely slowed by too little free space. Leave at least 20 percent free space on the drives that contain the virtual hard disk image.

8. Turn off visual effects in the guest OS—Guest OS visual effects consume CPU and memory resources. To disable unneeded effects on Windows XP, right-click on the guest OS's desktop, select Properties, Appearance, Effects, then clear the Use transition effects for menus check box. (The Windows 2000 procedure is similar.)

7. Preallocate the virtual hard disk—By default, the virtual hard disks of most VM products are configured to expand dynamically as new storage is required. Dynamic expansion saves disk space but slows guest OS performance. To eliminate this performance penalty, select the option to preallocate storage when the virtual hard disk is created.

6. Use raw or linked virtual hard disks—Using a raw or linked virtual hard disk (the terminology varies with the product) lets the VM directly read from and write to the disk, avoiding much of the overhead of other types of virtual disks. This technique can speed up applications for which disk performance is crucial.

5. Use Full Screen Mode—Running a VM in full screen mode rather than in a window gives you about a 10 percent performance boost by reducing the need to handle the host video I/O.

4. Create the virtual hard disk on its own drive spindle—Creating the VM's virtual hard disk on a different physical drive from the host's OS reduces drive spindle contention and improves the performance of the VM. If you run multiple VMs, place each VM on its own disk spindle.

3. Defragment the VM hard disks—Disk fragmentation occurs both at the guest OS and host OS levels, so disk defragmentation for VMs is a multitiered process. First, defragment the drive of the guest OS. (Some versions of VMware products also let you defragment the virtual hard disk, which can be done only when the VM is powered down.) Then, defragment the physical drive for the host OS.

2. Use a fast hard disk—Hard-disk speed is one of the biggest factors influencing VM performance. The faster the drive, the better your VM's performance. Use at least a 5400rpm disk on a laptop and a 7200rpm or faster disk on a desktop PC. For server consolidation, look for 10,000rpm or faster disks.

1. Maximize RAM—The amount of physical RAM probably is the biggest potential VM performance bottleneck. Allocate adequate RAM for the guest OS—at least 128MB for workstations and 256MB for servers. If you run only one VM at a time, consider giving it half the available host memory. VMs can use only physical memory, so you need sufficient physical RAM on the system. All the recent VM product releases support 3.6GB per VM, so maximize your host RAM.