I bought less than a month ago a Mac Book Pro retina display, 3 GHz processor and a 500Gb HD. As my previous old Mac Book Pro had a 320 Gb HD and it was really full, I did not migrate all the data, I did I clean install and I was watching somehow carefully the storage, as I am using a fairly big amount of images (and music) and I was deciding which way I could better manage them, between my external storage and the internal storage Now the problem is: until a week ago I had abt 200 Gb taken, 300 Gb free. Then, suddenly, checking the system info I noted I had 265 Gb used, 235 Gb free, without any apparent reason as I did not store more data. In that moment I did a trial install of Little Snitch, which I then uninstalled, but it should have nothing to do with it. Checking for the cause of it I found out a large amount of old email were downloaded to Mail from Gmail servers, and I deleted them. Now the situation that leaves me quite astonished is that on Finder window, in the Status Bar below, it shows 320 Gb available, while in the system info as well as in the Disk Utility it shows "Used 265 Gb" (I round up the digits) and "Available 235 Gb"... Looking in "About This Mac" --> "More Info.." --> "Storage", there is a detail of the kind of usage of the solid state memory and there is a "Backup" which is 85 Gb. If I deduct it from the used storage I have exactly the right space that I can see free in the Finder window. I tried to look is I could locate this "Backup" and I cannot find it. If I look in the root of my HD I basically have 4 directories which are: - Applications - Library - System - Users If I get the info abt them and I sum it up it comes exactly to the 180 Gb which are supposed to be used. I also tried to look for ALL file putting them in order of size, and I did not fin anything abnormal nor any huge file stored. Finally I can see this Backup only in the Disk Utility, and in no other place, and I changed its size. Can somebody explain it?