I am trying to understand how you need to set things up when trying to run Windows from a Mac (using Bootcamp / Parallels). I understand the differences in terms of Bootcamp requiring you to choose at bootup versus running side by side with Parallels but I want to understand the implications around HD and RAM.

So lets say I buy a Mac with 512 GB SSD and 16 GB of RAM. I see that if you want to install windows, you need to partition and allocation memory and disk space for Windows.

On Windows I would need to run:

  • SQL Server 2008
  • Visual Studio 2010
  • Microsoft Office and a few other pieces of propriety software

So my questions are:

  1. How do i decide how much space is allocated to Windows and once I decide that, can I change it in the future? I was thinking about allocated 100GB to Windows which seems like it should cover me.

  2. How do i decide what RAM is allocated to Windows. Can I change that on the fly in the future after that decision? Once I do this (lets say i allocate 8GB of RAM to windows), either through BootCamp or Parallels, does that mean that my Mac only will be able to leverage 8GB (since i have a total of 16GB) regardless if I am running Windows at that time or it only "takes" 8GB away when i start up windows.

1 Answer 1

  1. If you run Parallels off a disk image, you can expand that partition to as much disk space as you have available. All it requires is shutting down the VM. As far as I know you can't shrink a disk image.

    • If you're running Parallels off a Boot Camp partition, it's possible in some cases to expand that partition later on, using third party tools. This depends on how the other partitions on the disk are set up (typically a partition can be expanded to fill free space after it, but you can't change the starting point on the disk).
  2. How much RAM you allocate can be changed using Parallels. You simply shut down the VM, change the setting in Parallels and restart. This doesn't change whether you're using a disk image or a Boot Camp partition, but it's worth pointing out that if you boot from the Boot Camp partition (not in Parallels), that's running Windows directly and it will use all the RAM available to the system, like any other laptop.

    • The RAM allocated to your VM is only "used" when the VM is running. If you shut down Parallels, OS X can use the full amount in your system.
  3. How you allocate disk space and RAM depends on what you're doing with your VM, and what you expect to be doing with OS X while that VM is running. Think of it as configuring a whole new computer - you need a quantity of hard drive space and RAM sufficient for the tasks at hand. The easy part is that you can (mostly) change your mind later on if you guess wrong with a VM.

  • thanks for the response. Can you explain (or pass over a link if you have) that explains the pros and cons of using disk image versus boot camp partition . .
    – leora
    Aug 20, 2012 at 13:11
  • The Boot Camp option is really just there for people who are using Boot Camp already to run Windows directly on their Mac (with no virtualization). If you don't need to run Windows outside the VM, I'd suggest using a VM image. It's much more flexible and easier to back up. It's just a file on your hard drive, instead of a separate chunk of your hard drive (which OS X then can't use).
    – robmathers
    Aug 20, 2012 at 15:06
  • Thanks It mostly makes sense to me. However I'm a bit confused as to why I have wired memory at 10gb and literally 2 gb free while all I'm running is windows 8 as a VM on my mac and my apple mail. I'm scared to open photoshop in case it will all go haywire (pardon the pun). I have a MacBook Pro 16gb. I installed parralell and allocated 8 gb to windows 8 and 8 to Mac. On Mac I'm using photoshop and illustrator/ email iTunes and other minor On windows 8 i'm using office applications and Web Studio.
    – user44950
    Mar 12, 2013 at 14:04

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