File Structure

File Structure

1. Byte Sequence

   • The file is an unstructured sequence of bytes. In effect, the operating system does not know or care what is in the file. All it sees are bytes. Any meaning must be imposed by user-level programs. (UNIX, Windows)
   • Having the operating system regard files as nothing more than byte sequences provides the maximum amount of flexibility. User program can put anything they want in their files and name them any way that they find convenient.  The operating system doesn't help, but it also does not get in the way. 

2. Record Sequence

   • A file is sequence of fixed-length records, each with some internal structure. Central to the idea of a file being a sequence of records is the idea that the read operation returns one record and the write operation overwrites or appends one record.

3. Tree

   • A file consists of a tree of records, not necessarily all the same length, each containing a Key field in a fixed position in the record. The tree is sorted on the key field, to allow rapid searching for a particular key.
   • The basic operation is not to get the "next" record, although that is also possible, but to get the record with a specific key.