I use VMware Fusion (3.1.2) to run a Windows XP VM on my 2007 Macbook. Quite recently I was running short of disk space and was looking through my files to see where I could release some space. I was amazed to find that my virtual machine was taking up 33Gb on the disk. When you create an XP virtual machine, VMware will not let you allocate a disk size of less than 40Gb. I had assumed however that it would only take up space that it required. Although I use the VM everyday there is very little change to it. I simply have a standard XP installation along with a copy of Office 2007 pro installed and that is it. I do not keep any data files on the VM, preferring to keep them in OSX for ease of backup. Therefore, there is very little write activity within the VM just opening programs and reading files, and saving of work is done on to the OSX disk via the VM. A search around indicated that I could release some of the space by performing a normal disk defrag within XP and then using the shrink option in VMware tools. I did this and the VM size reduced to 12Gb. Still larger than I would expect but at least it gave me back 21Gb. Great, I though. I checked again about 4 weeks later and discovered the VM had grown again to 21Gb. I repeated the process and this time the VM reduced to 15Gb. During this time the only activity had been my normal daily use and downloading and installing some XP updates. Now 4 weeks on again the VM has grown to nearly 19Gb. For info I have around 23Gb free on a 250Gb drive, 4Gb of RAM with 768Mb allocated to XP I rarely see any page outs. If this was a windows machine I wouldnt expect to see the same level of growth, so this appears to me to be VMware inefficiently allocating data to VMDK files within the virtual machine, but to all you VM gurus out there I have two questions . 1. Can anyone give me a good explanation as to whats occurring and how I might be able to stop the growth? 2. In the coming months I am planning to migrate to the next gen MBP or an MBA with a smaller SSD so space will be more of an issue. Do parallels or Virtual Box manage their space better? Thanks for any replies, D.