Where does the "size" come from?

[hz363]

 Hello all:

    One problem disturbed me for long period.

     My OS or the the used space of C:\ partition is 40 GB. 

     The C:\ consists of 14-folder, including Progrem Files, Program Files(x86),

Users, Windows,..... 

     I select all the 14-folder and measure the size, by Properties, is 16.4 GB!

     You see, 40-16.4=13.6 GB. 

     Where is the 13.6 GB come from, what are they???  Could you tell me why?

                                                                                            -- Zhao

[WAWood · Accepted solution]

@hz363 

Basically, NO. Lots of the space used is in Hidden directories and files, which you will NOT be able to see.

However, if you are concerned about the lack of available disk space, here are some things you can do to recover some of the disk space:
http://www.tenforums.com/tutorials/3012-disk-cleanup-open-use-windows-10-a.html
http://winaero.com/blog/how-to-clean-up-winsxs-folder-in-windows-10/

Also, the community Win10 Forums has the following suggestions:
https://www.tenforums.com/tutorials/83441-free-up-drive-space-windows-10-a.html

[hz363]

   Dear WAWood: Your answer is very helpful. I need to explain my question more.

   My c-partition is 100 GB and installed the w10 OS as every one does. The whole OS was

consisted of 14-folder. The 1st folder is boot, the last one is Windows. the Program Files , Program Files(x86), users,... are between them. 

   My purpose is to measeure the used-space by the OS:

   Method 1:  L-C:/R-properities/used-space         ---->  40GB

   Method 2:  L-boot/ (Shift+R)Windows\properties\Size of all in C:      ----> 16.4GB 

   You see, the difference of both results are: 40 - 16.4 = 23.6GB.

    I think, The size of OS is divided into the 14-folders, the total size of 14-folder are

measured by the 2-method.  The both results 'should' be the same.

    The are quite different, what is my wrong?

                                                                                       -- Zhao