Virtual Machine Performance Myths, Debunked

Virtual machine’s capabilities are seemingly endless. Whether a Mac user needs Windows for gaming, Microsoft Office, or design programs – Parallels Desktop for Mac has you covered.

One important question remains: How do users know when to allocate specific resources to the virtual machine based on their needs?

It is a widely-discussed myth that a virtual machine needs ALL of the host machine’s resources in order to run effectively. This is simply not true.

In order to avoid mistakes with a virtual machine’s configuration, our team would like to shed some light on the matter by dispelling three common myths about virtual machine performance.

Myth 1: The more processors I assign to my VM, the better.

It sounds logical—more is better.

Well, that’s not exactly true.

One or two virtual CPUs is enough for most of the Windows applications you run. Assigning three CPUs can even slow down overall performance, especially if you have an older Mac model.

To see how many CPUs are assigned to your virtual machine, launch Parallels Desktop, and make sure your virtual machine is shut down.

Go to Virtual Machine Configuration > Select the Hardware tab > CPU & Memory.

You can then configure the number of processors (CPUs) to provide the appropriate number of computing resources for the workload you plan to run in the virtual machine.

In most cases, one or two CPUs provide the best performance with a virtual machine. Assigning several CPUs to your virtual machine may be required if outlined in your Windows program system requirements, but it also depends on your actual Mac hardware.

We unable to add to virtual machine more resources then your Mac has.

In order to add the necessary CPU numbers and get the best virtual machine performance as a result, we need to decide how we would like to use virtual machine: for gaming or just run any counting application like a QuickBooks, and also carefully read the application’s system requirements.

Myth 2: Maxing out my RAM makes my Windows VM run faster.

When you create a virtual machine on your Mac, Parallels Desktop allocates a certain amount of RAM by default to your virtual machine—the allocated amount depends on how much memory you have on your Mac and the user profile you’ve chosenduring setup.

Let’s make a short test.

Utilizing a MacBook Pro with 8 GB of RAM, Iopened a Microsoft Office programs and then started a resource-intensive program such as the Autodesk Revit Architecture application.

Firstly, I used 2GB of RAM and everything worked smoothly. Then, I added RAM to my VM and play Burnout Paradise with 4 GB RAM memory.

21 comments on “Virtual Machine Performance Myths, Debunked”

Brandon Champney
October 6, 2015 at 8:10 am

Hi, new to parallels, getting it soon. Will be running SolidWorks on Windows 7 a 3D cad program. It only uses one cpu so I am good with that. My question is my video card has 1500 mb ram and I have 16 gb system ram. Parallels pro allows you to set up to 64 gb vram which I’m not too clear about. Do I set my vram according to the video ram that I have or the system ram? Would it benefit me to get parallels pro instead of the basic parallels? Thanks
Brandon Champney
October 6, 2015 at 8:15 am

Hi, new to parallels, getting it soon. Will be running SolidWorks on Windows 7 a 3D cad program. It only uses one cpu so I am good with that. My question is my video card has 1500 mb ram and I have 16 gb system ram. Parallels pro allows you to set up to 64 gb vram which I’m not too clear about. Do I set my vram according to the video ram that I have or the system ram? Would it benefit me to get parallels pro instead of the basic parallels? Thanks
Lindsay
October 6, 2015 at 11:23 am

Hi Brandon,

In regard to your comment, “Parallels pro allows you to set up to 64 gb vram”, the term “vram” refers to virtual RAM, not video RAM. Apologies for the confusion there. Onto your question about how to set your virtual RAM – leave the video RAM setting for your Windows 7 virtual machine at the default, at first.

You should only increase the video RAM setting if SolidWorks won’t launch or performs poorly.
The memory for video RAM for the virtual machine comes out of your system RAM, not out of the RAM on your video card. Similarly, leave the RAM setting for your Windows 7 virtual machine at its default setting. You should only increase it if performance of SolidWorks is low.

Note that increasing the RAM setting of Windows 7 too much will result in poorer performance of Windows 7 and the Mac OS.

And finally, in regard to your question on purchasing Standard vs. Parallels Desktop Pro, it’s hard to predict. Certainly Parallels Desktop Pro is the safer choice, and one benefit is that you will be on a subscription (so you’ll never miss an OS update, etc. as long as you continue to renew your subscription), but SolidWorks should work fine on Standard. If performance on the Standard version is too low, we can help you test to see if Pro would increase performance – just let us know.

Hope that helped!

Lindsay
Riccardo Cambo
October 23, 2015 at 3:43 am

Hi, pretty silly question, if I dedicate 3 on 4gb of ram for Windows, when Parallel is closed I can only use 1gb ram for mac or It split only when parallel is open?
Lindsay
October 23, 2015 at 10:16 am

Hi Riccardo – the memory allocated to a virtual machine is only used when that virtual machine is running. However, we don’t recommend allocating 3 GB to a VM on a 4 GB Mac – you run the risk of “starving” your Mac of RAM, which could cause your entire Mac to run slowly. Just an FYI. Thanks for your question!
Bob
November 3, 2015 at 5:57 am

If this is true then why does it take windows 10 (under latest parallels version) 18 seconds to boot to login with 4 cores and 28 seconds to boot to login with 2 cores?
Lindsay
November 3, 2015 at 9:38 am

Hi Bob – it sounds like you might be experiencing a unique issue, so I recommend connecting with our Support team. The best way to reach out to them is on Twitter at the handle @ParallelsCares (https://twitter.com/ParallelsMac), or via private message on our Facebook page: https://www.facebook.com/ParallelsInc

Let me know how it goes! Thanks.
~Lindsay
Henry H.
December 20, 2015 at 6:12 pm

Hi, was wondering. is it possible that allocating too LESS ram memory for a vm will slow down the whole computer?

also, when is a vm not using the ram? if its just open but no programs are running, will it still keep it all? and what about suspended mode?
Lindsay
December 21, 2015 at 11:19 am

Hi Henry!

If a VM is not allocated enough RAM, the VM itself will be slow since it is constantly swapping in and out the required bits of code. This constant disk activity could conceivably affect other applications that are trying to access the disk.

When a VM is started, its allocation of RAM is dedicated exclusively to that VM. This RAM is unavailable to other Mac apps or other VMs. Even if the VM is doing “nothing”, this RAM is still unavailable to other Mac apps or other VMs. When a VM is doing nothing, the use of the CPU is basically zero, but the RAM is still exclusively dedicated to the VM.

Unless you have quite unusual needs in the VM, you should use the default amount of RAM. This will give you the optimal performance both in the VM and in the Mac.

Hope that helps. Thanks!

Lindsay
protez saç
November 14, 2018 at 6:58 am

I usually follow this kind of subject. In the form of a nice chat, the question is answered. I think it’s successful.
ASHISH TIWARI
August 7, 2019 at 12:20 am

I have a question regarding the Pro edition of Parallel desktop.
I run CFD simulations using openFoam for which I have installed linux ubuntu 18.04 LTS. I have a macbook Air and I think it’s not a good choice for meshing and running heavy calculations. I read that the Pro edition offers 128 GB virtual memory. Is it only useful for people with workstations ?
Kayla Myrhow
August 12, 2019 at 11:21 am

Hey there Ashish. We have thousands of users who use Parallels Desktop Pro Edition and do not have a workstation. iMac Pros, Mac Pros, and other devices often have larger amounts of ram installed to utilize the hardware or software they’re looking to virtualize. Don’t be shy – reach out if you have any more questions! kayla@parallels.com, Audience Marketing Manager.
Sasan
June 30, 2020 at 4:16 pm

Hello,
I have an old Macbook Pro (Late 2008) which has a dual core CPU and 8 GB RAM.
I always assign 1 core to virtual and leave one core for OSX. Also, I give the virtual 2-3 GB RAM and 256 MB video.
Can I assign both cores and full video RAM to the virtual machine so the computer shares everything with the virtual machine? If I do this, will I harm the computer? My life depends on this Mac.
Beatrice Vogel
July 6, 2020 at 1:25 am

Hey Sasan, We recommend you assign maximum half of the cores and half RAM to your VM for best performance. However, you can “play around” with it and see how it works best for you – you won’t harm your Mac as you can always change the settings. Let us know if you have further questions. Thanks
David
July 22, 2020 at 10:04 pm

Curious if this info is still valid in 2020 with v15?
Beatrice Vogel
August 20, 2020 at 5:30 am

Hey David, Thanks so much for reaching out. We just updated this blog post :-). Let us know if you have further questions or need additional tips. Thanks and have a nice day.
Fred
August 28, 2020 at 10:33 am

Half an article. Just stops mid-flow on RAM topic. I have a dual-core i7 3.5GHX Macbook Pro with 16GB RAM. I run Windows home in parallels 16 using 2 processeors and 4GB of RAM. I only run Outlook in Windows. The moment I start the VM the macbook fan comes on and mac apps noticeably slow down. Outlook frequently goes into ‘not responding.’ Frankly, that’s why I stopped using windows a decade ago. The point I’m making is that parallels isn’t a panacea. It will take resources away from your Mac and because mac resouces are being shared across 2 OSs, EVERYTHING slows down. If you’re going to run Parallels at all, even for a low usage windows app, the very fact that you are running windows is going to slow down your Mac. Answer. Gtet a really big spec Mac or kick windows completely into touch.
Beatrice Vogel
August 31, 2020 at 3:12 am

Hey Fred, Thanks for your message. Our support team is happy to help you with this. There are several reasons why it doesn’t work properly for you. Please reach out to them on Facebook https://www.messenger.com/t/ParallelsInc, Twitter https://twitter.com/ParallelsCares or any other of our support channels: http://www.parallels.com/support/. Any further questions let us know. Thanks
David
September 1, 2020 at 1:33 pm

No reason this shouldn’t just work. No one is going to make the effort to contact support to find out why the article is cut off. Have the support team fix it.
Asif
September 3, 2020 at 8:35 am

I have a mac book pro 2020 i5 quad core 8GB RAM and 256GB SSD. I have read that Parallel Desktop Pro offers 128Gb vRAM and 32 vCPUs. Can you please help out how is this going to work on my machine? I thought a VM would use Host machine hardware? Also is there a link for Parallels desktop 15? seems like 16 has lots of issues out there.
Beatrice Vogel
September 18, 2020 at 2:51 am

Hey Asif, Thanks for your message. The amount of memory you can assign to a virtual machine depends on the total amount of RAM your Mac computer has (to check Mac memory click on Apple logo > About this Mac). It is recommended to assign not more than half of your Mac’s memory (RAM) to a virtual machine. And if you want to run multiple virtual machines simultaneously, it applies to all of their memory combined. In Pro Edition you can assign up to 128 GB of memory. Feel free to test Parallels Desktop 16 for Mac for free: http://www.parallels.com/try/pd. If you have any further questions let us know 🙂