After a fresh Windows x64 Boot Camp install on a 16GB rMBP, I noticed that 28GB of precious SSD space was already taken. Since the Boot Camp partition was relatively small, I wanted to recover that unavailable space. Turns out it's due to Windows' Hibernation and Virtual Memory (pagefile). Hibernation reserves a file that's 75% the size of total RAM, and virtual memory reserves a file equal to 100% total RAM. So for a 16GB rMBP, Total used = (16*0.75 + 16) = 28GB, before even starting to use Windows. Here's instructions on how to recover the space. http://danalexander.org/2012/07/macbook-pro-boot-camp-disk-space-recovery/ Disabling hibernation is fine for most people, so long as you don't use Windows for work (ie. you won't lose any sleep over the laptop shutting down without saving if the battery dies). Lastly, please don't try to disable/customize your pagefile if you're unsure about something. I hope this helps anyone trying to do the same thing.