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
Make sure you're using the latest build for your version of Parallels Desktop:
- On the OS X menu bar go to Parallels Desktop > click Check for updates. Download and install the updates if available.
Try not to run several virtual machines at once; each consumes considerable resources and may slow down overall Mac OS performance.
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 performance.
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
Note for Parallels Desktop 10/11 users: Make sure that the option "Real-time Virtual Disk Optimization" is disabled:
Go to Actions > Configure > Options > Optimization > disable 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.
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 battery power, 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 tab > 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, two CPUs will provide optimal performance. Assigning more than two CPUs for the virtual machine may cause performance degradation on the Mac side.
NOTE: Please check with guest OS system requirements. Make sure that system requirements are fully met. For instance, in case of Windows 10 x64 OS one should have at least 2 CPU's and 2 GB of RAM assigned to the virtual machine. Please check with official system requirements for the guest system you are planning to install.
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.
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.
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