To save disk space, the Windows 10/8/7 operating system allows you to compress files and folders. When you compress a file, using the Windows File Compression function, the data is compressed using an algorithm, and re-written so as to occupy lesser space. When you access that file again, the data has to be again decompressed first before you can access it. Thus reading compressed files require more time and consume processing power too.

In Windows 7, the Compress Old Files option was removed from the Disk Cleanup Utility. This was presumably done since; now, large hard disks have become easily and cheaply available. Moreover compressing files did take a lot of time and therefore delayed the disk cleanup process. Windows has had no way of knowing which files it was compressing and compressed all of which had not been accessed for a particular period. This was not good as many times this could hit performance. This option was therefore removed from the disk cleanup utility.

In these days of large and cheap hard disks, many of us may not choose to use this feature – preferring instead other ways of freeing up disk space or using CCleaner, Quick Clean, or using some good free junk cleaners. But should you wish to compress files, this is how you can do it.

How to compress a file or a folder

To compress a file or a folder, right-click on and the file or folder and under the General tab, select Advanced.

Here check the option to Compress contents to save disk space and click Apply/OK. Windows will start compressing the contents. You can then show Encrypted or Compressed file names in color if you wish.

How to compress a Drive

To compress an entire Drive, right-click on the Drive, and under the General tab, check the option to Compress this drive to save disk space. Click Apply/OK.

While this may not apply to us now, it is good to know that you can compress contents only on an NTFS partition. You will not see the Advanced button if you are not on an NTFS drive.

File Compression Behavior

If you move a file from a DIFFERENT NTFS drive into a compressed folder, it is also compressed.
If you move a file from the SAME NTFS drive into a compressed folder, the file retains its original state, either compressed or uncompressed.

Do note that files and folders that are compressed using NTFS compression cannot be encrypted. You cannot further compress again a file that has already been compressed once. It’s not going to help much anyway.

Do Not Compress the System Drive

A Golden Rule! Never compress the C drive or System Drive. System drive compression could cause a lot of problems including causing driver installations to fail. And even if you still do decide to compress the system drive – DO NOT compress the root directory, and DO NOT compress the Windows directory. Doing so could even render your Windows computer un-bootable!

It was just the other day that my neighbor’s little daughter came running to me telling how she had compressed the C drive on her dad’s computer, to save space – and how now the computer was not starting. Well, her daddy came to know right away, and they decided to reinstall Windows…

But should you face this problem, you can check back tomorrow to find out what to do if you find that your Windows computer will not boot because you compressed the system drive.