When most people think of reading and writing application data, they almost instinctively think about large relational databases such as SQL Server or Oracle, or flat-file databases like Microsoft Access. Even when surrounded by all of that database power, applications still need to read and write data from regular files on disk.
This chapter introduced you to the concept of streams, the basic unit of I/O used throughout the .NET Framework. You can use streams to access data for virtually any underlying source, even if that source is entirely in memory as in the case of the MemoryStream class.
Finally, this chapter showed you how to work with the operating system itself to manipulate directories and files, as well as obtain detailed information about files on disk. In addition, you saw how to use isolated storage to allow your application to store user data in a way that is easy to use and doesn't violate CLR security policy for untrusted applications.
Whether you are creating large or small applications, Windows or web, you will undoubtedly find that the information in this chapter on streams and basic I/O is useful and applicable.