Ssd Memory Mismatch On Os X 10.9.4 (or "weird Math")


Hello everyone!

I have a 128gb MacBook Pro, and I've noticed one weird thing about its memory monitoring. I downloaded about 10 programs and some of my multimedia, which size must be about 40-60gb. So, "about this mac" says that I've got 140gb of programs (what???), 44gb of archives (which I actually store on extended HDD), 12gb of multimedia (well, this is true), and I STILL got 21gb of free memory.
I've got a little surprised, but then I looked on "properties" of the disk, and it says, that it got 53gb of files and 67gb is available (wow o_O). Well, ok, it really seems like a truth.
But I didn't stopped, and then made my own calculations! So I checked "properties" of each folder on disk (libraries, users, system etc.) and calculated their sizes. In the result, the size of all files on disk was 66,08gb...

As you can see - I am confused. Can you tell me something about this mess? How many space available I've got for real? Or maybe recommend some programs for disk monitoring?
Screenshots of "about my mac" and disk properties are related.

P.S. I am not native English speaker, sorry for the mistakes.


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