Question:

Could you elucidate the distinction between a folder’s reported size and its actual ‘size on disk’?

Answer:

refers to the actual amount of data contained within the folder. This is the sum of the sizes of all the files inside the folder as you would see them if you were to add up their individual sizes.

Size on Disk

, on the other hand, is often larger than the reported size. This discrepancy arises due to the way file systems store data. Hard drives are divided into sectors, which are further grouped into clusters. Each cluster is a fixed size, and the file system can only allocate space in whole clusters, not partial ones.

For instance, if a file system uses 4KB clusters and you have a file that is 1KB in size, it will still occupy a whole 4KB cluster on the disk. If you have multiple such files, each will take up a 4KB cluster, leading to a situation where the size on disk is significantly larger than the reported size.

This means that even if a folder contains small files, the size on disk can be considerably larger due to this minimum allocation unit, or cluster size. Conversely, if a folder contains fewer, larger files that neatly fit into the cluster size, the size on disk might closely match the reported size.

Understanding this distinction is crucial when managing storage on a device, especially when dealing with a large number of small files, as it can affect how much actual disk space is being used. It’s also important for optimizing storage, as sometimes changing the file system or cluster size can lead to more efficient storage usage.

In summary, the

reported size is the sum of the actual data, while the size on disk

reflects how that data is physically stored on the medium, influenced by the file system’s cluster size. Knowing this can help you better manage your computer’s storage and ensure you’re not surprised by a disk that fills up faster than expected.