What is the difference between internal tables and extract datasets?

• The lines of an internal table always have the similar structure. By using extract datasets, you can handle groups of data with dissimilar structure and get statistical figures from the grouped data.
• You have to describe the structure of the internal table at the starting. You need not describe the structure of the extract dataset.
• In contrast to internal tables, the system partly compresses precise datasets when storing them. This decreases the storage space required.
• Internal tables need special work area for interface while extract datasets do not require a special work area for interface.