For a very long time I don't know that in Windows OS, there is a technology called 'hard link'. One of the reason is that I usually just use FAT file system and only the NTFS support hard link.

The first time I know about hard link is when looking for information about winsxs folders. All the dll files in System32 are actually hard links point to winsxs folders.

 
C:\Windows\System32>fsutil hardlink list accessibilitycpl.dll
\Windows\System32\accessibilitycpl.dll
\Windows\winsxs\x86_microsoft-windows-accessibilitycpl_31bf3856ad364e35_6.1.7601.17514_none_5b652abeb21da986\accessibilitycpl.dll
 

The hard link was first introduced in unix like OS. Every Linux savvy should very familiar with hard link. But for windows user, many people may never heard of it.

Put it simply, for a file, when you copy and paste it, it will occupy double disk space, when use hard link, you only copy an index, now you get two file share the one storage space. Delete anyone of them don't affect another file, change anyone of them , another also changed.

Check file property of anyone of them, it shows that both of them accupy disk space, but actually they only share the same space.

Suppose you have file that size is 50MB, then create a hard link for the file, if you select the two files and check the total size, it will be 100MB. That means even Operating System can not tell which one is hard link and which one is real file. I think that why it called "hard". For soft link, if you delete the original file, the link will stop working.

Create hark link, your file system should be NTFS based. The command mklink can create hard link:

 
echo hello world > aa.txt
mklink /H link.txt aa.txt