Microsoft Windows Installation: 2 GB Became 18 GB
I found this by accident!
We use Ubuntu and Linux Mint on all our computers in the office. However, because our accounting software – Simply Accounting – only runs in Microsoft Windows, we installed Microsoft Windows on some computer inside Ubuntu/Linux Mint via Sun Microsystems’ VirtualBox. Yes, you can run Windows XP or 7 inside a Linux PC – not dual-boot – but run Windows XP or 7 via VirtualBox just like running a normal Linux program. And you can even move the entire Windows install to another PC without re-install.
Last weekend we chose to change one of our computers from Ubuntu to Linux Mint and this computer had Windows XP installed inside Ubuntu via VirtualBox. BTW, we did notice that Windows run very slow on this computer – we did some cleaning and run disk defrag but it still run slow. Anyway, because of this OS change, we backed up everything, including the .VirtualBox folder which contains this file winxp.img, the virtual file for Windows XP. We did notice that this winxp.img file is very big, about 18.3GB, which we thought normal initially.
After changing the OS for this computer from Ubuntu to Linux Mint, we tried to restore everything including Windows XP in VirtualBox. However, we could not get VirtualBox to use the huge winxp.img file we backed up together with all other files and folders in the .VirtualBox folder.
Having searched and tried very hard to re-use this huge winxp.img file but failed, we had no way but to re-create a new virtual disk and then install Windows XP fresh on that virtual disk. Realizing the old Windows XP image is 18.3 GB, we created the new virtual disk to be 40 GB and then installed Windows XP fresh and then installed all the same programs in it, just as in the case of the old Windows XP installation.
Then we found something that really shocked me. After we finished the installations of XP and all programs in it, we realized the new winxp.img file is not or even close to 18 GB – it is only around 2 GB!
This means that a fresh installation of XP and the same programs in it uses only 2 GB disk space while the same XP system used for a year or so grew to such a big size of 18 GB!
We understand that the browser surfing could accumulate a lot of cached files and a lot of other unused files could stay inside XP. But still 2 GB vs 18 GB is a huge gap. This may explain why Microsoft Windows becomes slow and slow with time.
BTW, the freshly installed XP inside VirtualBox run much faster than the old copy. But we worry how soon this 2 GB installation will grow to 18 GB or even close to 40 GB that we have set it for 
