Difference Between Disk Free Space & Used Space

September 2016

Have you ever wondered why the free space available on your hard disk doesn't always match up with the amount of free space that comes with your computer? This mismatch can be quite frustrating, especially when it requires having to calculate remaining storage space for every small download.

This article will walk you through some of the basic differences between provisioned space (or the storage space technically available on your computer) and free space (or the amount of storage space left on your device) and give you tips on how you can maximize space on your PC's hard drive.

Provisioned Space vs. Free Space

Hard disks are divided by allocation units, called clusters, which represent the minimum size occupied by a file on a hard disc.

An operating system uses blocks that compile several sectors (between one and 16 users). Each cluster will occupy several of these areas on your hard disc. Depending on the file system you're currently using and the overall size of your disc, clusters may occupy a considerable amount of space.

Each cluster contains data as a single file. Therefore, whenever your system saves a file, the data is written successively into the empty clusters — as soon as the first cluster is "full," the system moves onto the second cluster, followed by the third, and so on. For example, if you were to save a 6 KB file onto a system that uses 4 KB clusters, one and a half clusters would be used to store your file. You can manage the size capacity of your files by making all file sizes equal to that of each cluster.

We should not forget that the operating system also uses part of the disk space to manage all files (FAT structures, structures MFT system NTFS Alternate Data Streams, etc.).

Maximize Free Space on Your Hard Drive

In order to maximize the free space on your hard drive, we recommend that you reduce the number of small files on your computer (i.e. rid your computer of any folders that contain small files that are not often used or zip your files).

NTFS manages more small files in large numbers specifically on high capacity hard drives. It is therefore more practical to use NTFS rather than FAT, as the NTFS file compression can be used to reduce the space occupied by files. Keep in mind that, if files reduce a computer's performance, it will subsequently reduce the occupied space.

We don't recommended that you compress files that you use often, and it is never a good idea to compress your system files.

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