During the original installation of Windows XP on my computer the hard drive was partitioned into a 35 GB system partition (for the operating system and programs) and 170 GB data partition. This has worked well for the past two years, and I do regular housekeeping on the computer (such as defragmentation, antivirus scans, and antimalware scans). Last time I checked there was 16 GB of free space on the C drive and plenty of room on the D drive. However, suddenly the C drive has become full even though I cannot find any extra data on the drive. In fact, I had to uninstall several programs just to give the defragmentation utility enough space to run! Now that the defragmentation utility has been able to scan the computer it shows masses of red (non-contiguous) files and almost no white (empty) space. Do you have any ideas of what could be occupying all the free space?

In this situation it is not surprising that the defragmentation utility is reporting significant fragmentation on the drive, since there is so little available space that files are being placed wherever free space is available, which is not necessarily contiguous with the other portions of those files. For those who are not familiar with the concept of data fragmentation (and defragmentation), data stored in a computer hard drive is comprised of blocks. All of these blocks together form the piece of data, such as a file. When a hard drive has plenty of free space then all these blocks which comprise the one piece of data can be stored contiguously. As files are added, removed or have their size changed (which is happening continuously on a computer) then the vacant space on the hard drive becomes more patchy as some blocks may be removed and others are added. Therefore, potentially data can no longer be stored contiguously and some blocks may need to be stored in other parts of the hard drive where there is available space. This is called fragmentation as the blocks for a piece of data have now become fragmented. This can result in performance degradation since instead of the hard drive being able to read all the data neatly one block after the other it could instead have to read different data blocks from different locations all over the hard drive. Since this requires the drive to seek and read completely different locations each time, there is a performance hit. Now, getting back to the original issue of a significant level of fragmentation, because there is so little free space available it is highly unlikely that there is sufficient contiguous space to store files on the drive and therefore they are being written wherever space is available, resulting in the fragmentation.

We need to determine why so much space has been occupied on the hard drive in such a short period of time. In many cases this is due to a small number of large files finding their way onto the computer, although it is equally possible that a large number of small files could also be taking up the space. Before going any further I would suggest that you complete a full antivirus and antimalware scan of the computer, in case the space consumption has been due to something malicious on the computer. I would recommend that you scan the computer using AVG Free (free.avg.com) or Microsoft Security Essentials (www.microsoft.com/security_essentials) and also then use Ad-Aware Free (www.lavasoft.com), Spybot Search & Destroy (www.safer-networking.org), and Windows Defender (www.microsoft.com/downloads).

If the computer comes back with a clean bill of health following the scans then we can assume that something (which is hopefully not malicious) is not taking up all the space on the hard drive. So we now need to determine what is actually occupying that space. Unfortunately, Windows does not provide a convenient listing which includes the size of each folder, as in fairness this would be quite difficult. In order to calculate the size of a folder the size of all the files within that folder (and its sub-folders) need to be added together. Therefore, the long way of finding out this information would be to look at the properties of each folder located in the root of the C system drive and check whether any are taking up an unusually large amount of space. When you view the properties of a folder you will notice that the size of the folder counts upward as each file within the folder is being parsed for size and then added onto the total size for that folder. Once you have found a folder which is occupying a large amount of space you can then drill-down into that folder and look at the size of each sub-folder, and check which one(s) is taking-up all the space. As you can see, this would be a rather time consuming process and also is not guaranteed to be fool-proof as you could easily miss the folder and files which are taking up all the space. Therefore, we should try to find a better tool to determine the size of the various folders on your computer.

A very good tool for determining the size of folders and tracking down where all your free space on the computer has gone, is TreeSize. There are several versions of TreeSize available, but TreeSize Free (www.jam-software.com/freeware) should meet your needs well. This will provide a neat listing of the size of each folder and all its subfolders and files. This will allow you to see the size of each folder at a glance, and also sort the folders so that they display in size order (allowing you to immediately identify which folders are occupying the most space). If you really like this tool you can also look at TreeSize Professional (www.jam-software.com/treesize) which includes more advanced features that may be useful for your purposes.

In either case, once you have used TreeSize Free or TreeSize Professional to determine the size of the folders on your computer you should have a good idea as to the largest folders which are occupying space. At this point you will need to make a decision as to whether the files occupying the space are needed or not. Unfortunately you are the only person who can make this decision at this point, since I do not know which files are going to present themselves as taking up the space. However, if you are unsure whether these files should be retained or removed then please feel free to contact me again with the names of the files, and the location in which they were found and I will be happy to do some research on those files and their purpose.