Why on the hell i re-use the same 4GiB VDI on all Windows machines? Easy, it is a MBR disk with a FAT32 partition where i put pagefile.sys, since it is inmutable all virtual machines will create a file on their snapshot folder where they store the changes, and that get lost on next boot, so i do not need 4GiB for each guest stored on the host disk, just only one... that way i save a lot of GiB since i have more than 20 different windows for testing apps i develop for my own, all combinations of (XP, Vista, 7, 8, 8.1, 10)*(32Bits, 64Bits) * (Just as is on first install, after each ServicePack, after full windows update), i get a lot, lot of guest... so on all of them i share the inmutable 4GiB VDI for the virtual ram (pagefile.sys).