When magnetic tapes took over, it became possible to store more than 80 characters about a given customer together in one unit called a record. Because tape drives took considerable time to start and top and required an inter-record gap, for efficiency, groups of unrelated logical records were grouped together into one physical record. Logical records came known as records, and physical records as blocks.

C’s struct described the structure of one record.

Because the format of binary records depends on the platform, the original fiercely-platform-independent Java had no way of directly reading and writing records, other than object serialisation where all the fields in an object and dependent objects were individually packed up and written as a lump.

With the nio classes, Java defines a platform independent format for binary records, and a way of reading them as a lump. It deals with the platform specific conversion details only when you access a field in record.