What has changed Finder list view in Lion to make "Calculate all sizes" exponentially faster? Since way before Mac OS X came on the scene, we have been able to ask the Finder to Calculate all sizes in order to determine the sum total of readable file size space contained in each folder for the Finder window in question.



I have tested List view sizing of folders on several Macs where it doesn't matter if an SSD is present or not, but Lion is so fast at calculating sizes I am curious if there is some new caching data structure or if Finder is using the metadata information from Spotlight or a similar database to speed up this calculation immensely.
Before Lion, the File Size column in Finder.app would display the size each file requires on the hard disk, not the exact file size. For example, 1 byte files were displayed as 4 KB because they do in fact take up 4 KB of space on a HFS-formatted system. There was no easy way to see the actual file size of 1 byte, other than opening File › Get Info (or using a different app, like Terminal.app and then using ls -lsa, or a Finder.app replacement like TotalFinder.app).

(Back in the day, I reported this as bug 8926275 on bugreport.apple.com.)

As of Lion, this behavior has been corrected, and the File Size column will now show the exact file size for each file rather than the size it allocates on the hard disk (which depends on the file system anyway).

Since these sizes are the same numbers you’d get from the ls binary in Terminal, they’re much more efficient to calculate.