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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


Virtual machine performance is slow either from the start up or while using a certain application. There could be several reasons for the slowness.


  • Using the old (not the latest) build of Parallels Desktop application.
  • Lack of resources assigned to the virtual machine.
  • Multiple Anti-virus programs or virus.
  • Presence of unused files in the virtual machine.
  • Too many or conflicting start up items.
  • Too many virtual machines running.
  • Enabled option 'Real-time Virtual Disk Optimization' (for Parallels Desktop 10)


This article below will provide you with several steps and hints on how to increase the performance of your Virtual Machine:


  1. Note for Parallels Desktop 10 users: Please make sure that the option 'Real-time Virtual Disk Optimization' is disabled*:

    • Go to Actions > Configure > Options > Optimization > Free Space: Real time virtual disk optimization.

    • *Enabled option 'Real-time Virtual Disk Optimization' may slow disk perfomance up to 30% (at the moment of compacting, not constantly). If host has SSD disk, feature will be enabled by default for all the VMs (but will work only if it is compatible with guest OS)
  2. Please make sure, that you are using the latest build for your version of Parallels Desktop:

  3. Try not to run several virtual machines at the same time, because each virtual machine consumes a considerable amount of resources and can slow down overall Mac OS performance.

  4. Make sure Time Machine backup is not being performed at the moment. The backup creation process while running may slow down overall system performance.

  5. In Parallels Desktop menu bar go to Parallels Desktop > Preferences > Advanced Make sure detailed log messages option is not enabled.

    NOTE: enabling this feature is only necessary while troubleshooting issues related to your Virtual Machine and it may be requested by Parallels Support representative.




  • 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 checkboxes.

    In case you are not running on batteries you can also turn on Better Performance option.


  • Go to Sharing > Disable Smart Mount.
  • Go to Hardware tab > Boot Order > make sure that Hard disk 1 is the first boot device from the top by re-order the devices using the arrow keys on the right hand side of the pane.

  • Go to Virtual Machine menu > Configure > General

    Here you can adjust the number of CPUs and memory assigned for the Virtual Machine. However please note that virtual CPUs and memory are not acting exactly the same as the real hardware CPUs and memory installed on a PC or Mac. ( Please note that in Parallels Desktop 10 these settings were moved under Hardware tab )


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

    • In most cases one CPU will provide better performance. Assigning several CPUs for the Virtual Machine may be required in case you run some software that performs a lot of mathematical calculations, such as scientific software or On-line Trades software.

    If you are not sure if the application you want to run in the Virtual Machine requires more than one CPU just test it with 1 CPU assigned for the Virtual machine. If you see that your Virtual Machine is slow you can try with two or more CPUs.

    • Keep within the Recommended memory range for most cases. More memory assigned for the Virtual machine will not always make it faster.

    • Minimum of Memory assigned to the Virtual machine should be equal to the minimum recommended memory indicated in the System Requirements of the Guest Operating System you run.

    • Maximum of Memory assigned for the Virtual Machine should be calculated from the amount of memory actually used by the operating system when you normally work with it.

    Please select the optimal size of RAM via this article: How much memory should I assign to my Virtual Machine?.

    Video Memory

    You can configure video memory in virtual machine configuration > Hardware > Video.

    Virtual machine has virtual memory allocated from Mac RAM. Virtual video memory almost does not depend on Mac video card and Mac video memory. While operating with virtual machine, the textures and the other Guest video data are transmitted to the Host OpenGL. OpenGL decides itself whether to collect this data in the Host RAM or in the Host video memory.

    Generally, 256 MB of video memory is enough. Sometimes, Parallels Desktop recommends to increase it to 512 MB, e.g. when retina is enabled and there is an external monitor. Certainly, you can increase the video memory to 512 MB or more, even if there are no retina and external monitor, but it leads to some consequences:

    • Virtual machine consumes more Host RAM.

    • Windows apps are smart, they adapt to larger amount of video memory and start to load textures with higher resolution. It increases the Guest RAM consumption since Guest DirectX, relatively speaking, keeps the copy of its resources in the RAM. Therefore, increasing the video memory, you should also assign more RAM to the virtual machine.

    • Mac OpenGL consumes more Host RAM since it also keeps the copy of its resources in the RAM.

    So, virtual video memory has triple prize for Host RAM.


  1. Start Windows Operating System and click Start > Run and hit Enter/Return > type %temp% and hit Enter/Return key on your keyboard > select all files under this folder and delete them permanently (Empty Recycle Bin).

  2. Click Start > Run and hit Enter/Return > type temp and hit Enter/Return key on your keyboard > select all files under this folder and delete them permanently (Empty Recycle Bin).

  3. Click Start > Run and hit Enter/Return > type recent and hit Enter/Return key on your keyboard => select all files under this recent folder and delete them permanently (Empty Recycle Bin).

  4. Click Start > Control Panel > Add/Remove Programs in Windows XP or Programs and Feature/ Uninstall Programs in Windows 7 and uninstall unwanted or unused applications.

  5. Free up some space in C: drive by deleting unwanted files or moving files from C: drive to other drive.

  6. Use Windows Task Manager to troubleshoot the performance issues. Go to Devices menu in Parallels Desktop menu > Keyboard > Ctrl+Alt+Del and follow instructions in this KB article:How to use and troubleshoot issues with Windows Task Manager.

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

Windows XP:

  • Click on Start > All Programs > Accessories > System Tools > Defragment.

Windows 7:

  • Click Start > in the search box type defragment and select the first program listed.

    For more info please read the Microsoft KB article.

  • Start defragmenting the hard drive.

Try removing Antivirus from Windows Operating System:

  • Start Windows OS and click Start > Control Panel > Add/Remove Programs in Windows XP or Programs and Features in Windows 7.
  • Locate the Antivirus installed on the system from the list and click on Uninstall/Remove.


You have a Windows 7 64-bit Virtual Machine. You use Microsoft Office Suite, FireFox browser and a couple of other applications on a daily basis. You need to calculate the optimal amount of CPUs and Memory that will provide the best performance for the Virtual Machine.

  1. Go to Virtual machine > Configure > General and make sure 1 CPU is assigned.
  2. Check how much Memory is currently assigned for the Virtual Machine. By default is 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. OK, let's start with it!

  4. Start Windows and launch all applications you use on the daily basis: lets start Microsoft Outlook (open several messages there), Microsoft Word (3 documents), Microsoft Excel (a couple of spreadsheets), Firefox (10 tabs), PowerPoint presentation, One Note, Windows Explorer window and Calculator. Now right-clik on Windows taskbar and start Task Manager, switch to Application tab and check how much CPU and memory is used in Windows. You may see something like this:


    We can see that all running applications and Windows 7 itself consume about 80% of memory and less than 1% of CPU.

    It means that 1 Gb of Memory and 1 CPU assigned for the Virtual machine are still enough for all those applications to run in Windows at the same time with good performance. However it may not be enough if you decide to play any flash game or watch Flash video on

    Having this information you can either keep the current settings or go back to Virtual Machine > Configure > General and add some memory.

    We would recommend adding not more than 0,2 Gb (256 Mb) or 0,5Gb (512 Mb) at a time.

    It will ensure 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 please refer to the following Knowledge Base article:

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