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How can I improve virtual machine performance on my Mac?

  • Parallels Desktop 10 for Mac
  • Parallels Desktop 9 for Mac
  • Parallels Desktop 8 for Mac
  • Parallels Access


Virtual machine performance is slow either from startup or while using a certain application. There are several possible reasons for this, such as:

  • Using an old build of Parallels Desktop, instead of the latest.
  • Lack of resources assigned to the virtual machine.
  • Multiple antivirus programs or a virus.
  • The presence of unused files in the virtual machine.
  • Too many or conflicting startup items.
  • Too many virtual machines are running.
  • Enabled option "Real-time Virtual Disk Optimization" for Parallels Desktop 10 (see KB 122668).


This article offers tips on how to improve the performance of your virtual machine.

Parallels Desktop Preferences

  1. Note for Parallels Desktop 10 users: Confirm that the option "Real-time Virtual Disk Optimization" is disabled:

    • Go to Actions > Configure > Options > Optimization > Free Space: Real-time Virtual Disk Optimization.
    • If the "Real-time Virtual Disk Optimization" option is enabled, it may slow disk performance up to 30% (at the moment of compaction, not constantly). If the host has an SSD disk, the feature will be enabled by default for all virtual machines but will work only if it is compatible with the guest OS.
  2. Make sure you're using the latest build for your version of Parallels Desktop:

    • In the toolbar, go to Parallels Desktop > "Check for updates."

    • Or download and install the appropriate version from KB 5802.
  3. Try not to run several virtual machines at once; each consumes considerable resources and may slow down overall Mac OS performance.

  4. Make sure Time Machine backup is not taking place while you’re running the virtual machine. The backup creation process may slow down overall system performancer.

  5. In the Parallels Desktop menu, go to Preferences > Advanced. Make sure "Detailed log messages" option is not enabled. Note: Enabling this feature is necessary only while troubleshooting issues related to your virtual machine, and it may be requested by a Parallels Support representative.

Virtual Machine Configuration

  • Open virtual machine configuration > switch to Options tab > Optimization tab > Set performance to "Faster virtual machine"; check "Enable adaptive hypervisor" and "Tune Windows for speed." If you're not running on batteries, you can also turn on the "Better performance" option.

    To know more about the "Adaptive Hypervisor" option, see KB 122828.

  • Go to Sharing > Disable Smart Mount.
  • Go to the Hardware tab > Boot Order, and make sure Hard Disk 1 is the first boot device from the top by reordering the devices using the arrow keys on the right hand side of the pane.

  • Go to Configure > Hardware > CPU & Memory (Configure > General in Parallels Desktop 9 and earlier). Here you can adjust the number of CPUs and memory assigned for the virtual machine. Note that virtual CPUs and memory do not act the same as the real hardware CPUs and memory installed on a PC or Mac. (In Parallels Desktop 10, these settings are in the Hardware tab.)

To achieve the best performance we recommend to follow these general tips:

  • In most cases, one CPU (two CPUs in Paralels Desktop 10) will provide better performance. Assigning several CPUs for the virtual machine may be required in case you run software that performs a significant number of calculations, such as scientific software or online trades software.

    If you're not sure if the application you want to run on the virtual machine requires more than one CPU, test it with one CPU assigned for the virtual machine. If your virtual machine is slow, try with two or more CPUs.

  • Stay within the recommended memory range for most cases. More memory assigned for the virtual machine will not always make it faster.

  • The minimum memory assigned to the virtual machine should be equal to the minimum recommended memory indicated in the system requirements of the guest OS you're running.

  • The maximum memory assigned for the virtual machine should be calculated from the amount of memory used by the OS when you normally work with it.

  • Choose the optimal size of RAM via KB 113649.

Video Memory

  • You can configure video memory in virtual machine's configuration > Hardware > Video. The virtual machine has virtual memory allocated from Mac RAM. Virtual video memory almost does not depend on the Mac video card and Mac video memory.

  • While you’re operating the virtual machine, textures and other guest video data are transmitted to the host OpenGL. OpenGL decides whether to collect this data in the host RAM or the host video memory.

  • Generally, 256 MB of video memory is enough. Sometimes Parallels Desktop recommends increasing it to 512 MB (for example, when Retina is enabled and there is an external monitor). You can increase video memory to 512 MB or more even if Retina and an external monitor are not in use, but this may have consequences:

    • Virtual machine consumes more host RAM.

    • Windows apps are smart—they adapt to a larger amount of video memory and start to load textures with higher resolution. This increases guest RAM consumption because guest DirectX keeps a copy of its resources in the RAM. Therefore, if you increase video memory you should also assign more RAM to the virtual machine.

    • Mac OpenGL also keeps a copy of its resources in the host RAM.

Internal Windows OS Improvement

  1. Launch the Windows Operating System and select Start > Run, then hit the Enter key.
  2. Type "temp" and hit Enter , then select all the files in this folder and delete them permanently by emptying the Recycle Bin.
  3. Select Start > Run and hit Enter, then type "temp" and hit Enter. Select all the files in this folder and delete them permanently by emptying the Recycle Bin.
  4. Select Start > Run and hit Enter, then type "recent" and hit Enter Select all the files in this folder and delete them permanently by emptying the Recycle Bin.
  5. Select Start > Control Panel > Add/Remove Programs in Windows XP or Programs and Feature/Uninstall Programs in Windows 7. Then uninstall unwanted or unused applications.
  6. Free up space in the C: drive by deleting unwanted files or moving files to a different drive.
  7. Use Windows Task Manager to troubleshoot performance issues. Go to Parallels Desktop > Device > Keyboard > Ctrl+Alt+Del, then follow instructions in this Microsoft KB article: How to use and troubleshoot issues with Windows Task Manager.

If performance does not improve, follow the instructions below to run defragmentation on the system:

Windows XP:

  • Select Start > All Programs > Accessories > System Tools > Defragment.

Windows 7:

  • Select Start. In the search box, type “defragment” and select the first program listed. For more information, read this Microsoft KB article.
  • Start defragmenting the hard drive.

Try removing antivirus software from the Windows OS:

  • Launch Windows, then select Start > Control Panel > Add/Remove Programs in Windows XP (or "Programs and Features" in Windows 7).
  • Locate the antivirus software installed on the system and click on “Uninstall/Remove.”


You have a Windows 7 64-bit virtual machine. You use the Microsoft Office suite, Firefox browser, and a couple of other applications on a daily basis. You need to calculate the optimal number of CPUs and amount of memory that will provide the best performance for the virtual machine.

  1. Go to Virtual Machine > Configure > General and confirm that one CPU is assigned.
  2. Check how much memory is currently assigned for the virtual machine. The default is 1 GB.
  3. Go to Microsoft web site and check the system requirements for Windows 7. It says 1 GB is the minimum required, so we’ll start with that.

  4. Start Windows and launch all the applications you use regularly: Outlook (open several messages), Word (several documents), Excel (a couple of spreadsheets), Firefox (10 tabs), PowerPoint (a presentation), OneNote, Explorer, and Calculator. Right-click on the Windows taskbar and start Task Manager, switch to the Application tab, and check how much CPU and memory is used in Windows. You may see something like this:

  5. We can see that all running applications and Windows 7 itself consume about 80% of memory and less than 1% of the CPU. This means that 1 GB of memory and one CPU assigned for the virtual machine are enough for all these applications to run in Windows at the same time and perform well. However, it may not be enough if you decide to play a flash game or watch a flash video on YouTube.

  6. At this point, you can either keep the current settings or go back to Virtual Machine > Configure > General and add memory. We recommend adding no more than 0.2 GB (256 MB) or 0.5 GB (512 Mb) at a time. This will guarantee that both your virtual machine and your Mac OS X are running at their optimal performance. For more information about CPU usage in Windows and Mac, see KB 112764.

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