Windows always slows down a lot if free space on system drive (the drive or partition Windows is installed on) falls below 10% of total disk space. So keep at least 10 GB free on 100 GB system drive, but no matter how small your hard drive is, do not let free space on your hard disk fall below 2 gigabytes to ensure there is enough free space available for updates and temporary files.
How much free space have I got on the hard drive?
Open (My) Computer or This PC from Desktop or Start menu/screen, or use keyboard shortcut Windows Key+E.
If you have this folder in Details, Tiles or Content view, you can just check what's written in the Free Space column of hard disk with Windows on it (usually Local Disk (C:) or Local Disk (D:)).
In Windows Vista, 7, 8 and 8.1, a good indication of disk space usage is also the Space used progress bar - if the bar is blue, you have more than 10% of free space on the drive; if the bar is red, you should free up some space on the disk.
In Windows Vista and 7, you can also click on a disk once and see Space free and Total space values in Details Pane in the lower part of the window. The Space used bar is also here to indicate the level of disk usage.
In Windows XP, right-click a disk and select Properties from the menu.
Then see what's written in the Free Space row.
Click to select the system drive (the drive where Windows is installed) in Windows/File Explorer, then right-click the drive and click Properties. In Windows XP, you can just right-click the drive; in newer Windows versions you must click it first.
Make sure General tab is open. Click Disk Cleanup.
Windows Vista will ask whether you want to clean up just your own files or files of all users on the computer. Click Files from all users on this computer.
Of course, Vista's User Account Control opens after this. Click Continue.
Windows will calculate what it can delete. This might take several minutes.
After it is ready, it presents a list of solutions.
You can safely check all items in the Files to delete list except for Office Setup Files (in case you have Microsoft Office installed) without losing anything important. You can also read Description text after clicking on an item in the list.
If you experience frequent computer crashes (aka Blue Screens of Death, BSOD) and restarts, do not select Memory Dumps - use free WhoCrashed for analyzing crash dumps and determining causes of problems. After the problems have been resolved, it is safe to remove the old memory dump files.
Windows XP offers to Compress old files - the files that have not been accessed or modified within last 50 days. You can use this option safely, but be aware that the process might take up to several hours to complete.
In Windows Vista, 7, 8 and 8.1, you should not tick the Thumbnails option. Thumbnails are small previews of photos and videos available on your computer. You see those preview pictures while you browse your Pictures and Video folders or libraries. Unless you have recently deleted hundreds of video and photo files, you should leave Thumbnails deselected, because Windows will re-generate these anyway the next time you browse libraries with photos and videos (and the process slows down folder browsing for a while).
Click OK to start erasing unnecessary files.
Disk Cleanup will ask for your confirmation. Click Yes or Delete Files.
The cleanup might take quite a while, depending on how much data is selected for deletion:
The Disk Cleanup window will disappear after the cleanup finishes. This leaves Disk Properties window open.
If you still have not enough free space on the system drive, click the Disk Cleanup button again.
Because Windows 7 and 8/8.1 do not delete temporary System Files, you need to click the Clean up system files button. This also requires administrative rights.
Again, Disk Cleanup will scan for the files that can be removed. This might take a minute or so.
Basically, you will have the same options as described previously and you can safely choose everything except Office Setup Files. Those users who have installed a Windows Service Pack will see an additional check box - Service Pack Backup Files. This one is safe to check in case Windows runs fine for at least a week after installing the Service Pack.
Windows 8 and 8.1 also offer to remove or compress old, outdated Windows Update packages. Tick the Windows Update Clean-up check box for this to happen. The same now applies to those Windows 7 Service Pack 1 users who have applied the KB 2852386 update.
Click OK to remove the unneeded files.
Disk Cleanup will ask for your confirmation. Click Delete Files.
As in previous example, the removal process might take several minutes and the dialog will close automatically.
As usual, the window will disappear automatically after the process is complete.
System Restore creates restore points for Windows and you can use these to restore your computer to an earlier state in case Windows stops working correctly. Still every restore point uses quite a chunk of disk space. If you happen to have a PC that is several years old, you can free up loads of disk space by deleting all restore points except the latest one.
Shadow copies are used for creating System Image backups and Previous Versions of files in Windows Vista and 7. These copies ensure that even files that are in use and locked get backed up to create a complete and restorable system image.
In Windows 8 and 8.1, Previous Versions has been replaced by File History that uses less space on system drive by keeping most backups on selected external drive.
First, make sure your computer is working properly and you have no need for using System Restore. Restart your computer and verify everything is working fine.
If Disk Cleanup window is not yet open, open Disk Properties, click Disk Cleanup and wait while the program calculates the space that can be freed by deleting temporary files.
In Windows Vista, make sure you use the Files from all users on this computer option in the prompt.
In Windows 7, 8 and 8.1, click the Clean up system files button first. Windows XP and Vista users should move on to the next step.
Now open the More Options tab. In the System Restore (in Windows XP) or System Restore and Shadow Copies section, click the Clean up... button.
Disk Cleanup asks for your confirmation, click Yes or Delete here:
Again, Disk Cleanup shows no dialog after completing the job. Close the Disk Properties window by clicking OK after the Disk Cleanup window disappears.
All NTFS-formatted partitions/volumes support file and folder compression. This works best with common document formats, such as Word and Excel files, text files and logs - the file size can decrease up to two times, sometimes even more. Picture, audio and video formats that are already compressed (such as JPG, MP3, MPG) and most executable files do not compress that well.
NTFS compression has nearly no effect on performance while free disk space might increase noticeably.
Please note that this feature has nothing to do with Compressed (Zip) Folders in Windows! NTFS compression leaves files and folders usable by Windows and programs after applying the Compressed attribute, while Zip folders archive these into a single file that can be used by archiving tools only.
You can normally get best results by compressing the folder that contains users' files - Documents and Settings in Windows XP, Users in Windows Vista, 7, 8 and 8.1.
You should never try to compress a whole system drive or Windows folder or its subfolders - this will make your computer unbootable!
First, close all open programs and documents. Open Windows/File Explorer using keyboard shortcut Windows Key+E and open the drive where users' files are. In Windows XP, locate and right-click the Documents and Settings folder. In Windows Vista and later, locate the Users folder, click on it once and then right-click it.
Select Properties from the menu.
Folder Properties window opens. Click the Advanced button.
In the Advanced Attributes window, enable the Compress contents to save disk space option. Then click OK twice to close this window and the Folder Properties window.
Windows will confirm attribute changes. Leave the Apply changes to this folder, subfolders and files option selected and click OK.
In Windows XP, file and folder compression starts.
In Windows Vista, 7, 8 and 8.1, you need to provide administrator permission next. Click Continue.
Windows Vista users must also click Continue in the User Account Control dialog.
As usual, several system files are locked while a user is logged on to Windows. Click Ignore All in the first Error Applying Attributes window.
The compression process might take from 5 minutes to an hour, depending on how many files and subfolders there are. After the progress dialog disappears, you'll notice that the Documents and Settings / Users folder is now blue (if the Show encrypted or compressed NTFS files in color setting is enabled in Folder options). This indicates that the item is compressed using NTFS compression.
To see how much disk space you gained, right-click the folder and select Properties again.
Check the difference between Size and Size on disk fields. In the example below, users had a few personal files only, but settings and temporary files were compressed from 766 to 576 megabytes (compression rate is almost 25%).
You can also compress Program Files and ProgramData folders, but never compress Windows folder or whole system drive! System files must be uncompressed while Windows starts.
By now you should have sufficient disk space on your hard drive. If not, use CCleaner to clean up leftovers from well-known programs.