From the publisher’s website:
JDiskReport provides different perspectives about your disk drives: absolute and relative sizes, size distribution, distribution of modification dates, and distribution of types.
Each perspective includes a pie chart, a bar chart, and a details table. You can choose to either show the file size or the number of files. Also, JDiskReport collects a list of 100 largest, oldest, and newest files.
The size perspective shows you how much space the files and folders consume on your disk drives. The size pie chart is probably the best to find monster files and folders. You can switch to the table view and toggle the display of files to get more detailed information about a folder.
The size distribution views help you to learn more about the different file sizes that exists on your hard disks. Look at these views to check whether the size distribution is what you expected it to be.
If you are in ‘Show file size’ mode, you can see how much space is consumed by large, medium sized, and small files. In ‘Show number of files’ mode, you see how many files are large, of medium size, and small.
The modification distribution views provide you with information about when how much space and how many files have been modified.
The type distribution statistics are collected from the file extensions that exist on the analysed file tree. You can see which file type consumes space and how many files of a given file type you have.