Structured Data can be stored in traditional database systems like- Oracle, SQL server, MS Access etc. It is stored in rows and columns. Most of the online application transactions are Structured Data. Structured data can be easily defined in a data model.
Unstructured data cannot be stored in terms of rows and columns. So it cannot be stored in traditional database systems. Generally, it has varying size and content. Some of the examples of unstructured data are log files, tweets, Facebook likes, Google search items.
Most of the Internet of Things (IOT) data is unstructured data. It is difficult to define unstructured data in a defined data model. Some of the software supporting unstructured data is: MongoDB, Hadoop etc.