<P> A file system consists of two or three layers . Sometimes the layers are explicitly separated, and sometimes the functions are combined . </P> <P> The logical file system is responsible for interaction with the user application . It provides the application program interface (API) for file operations--OPEN, CLOSE, READ, etc., and passes the requested operation to the layer below it for processing . The logical file system "manage (s) open file table entries and per - process file descriptors ." This layer provides "file access, directory operations, (and) security and protection ." </P> <P> The second optional layer is the virtual file system . "This interface allows support for multiple concurrent instances of physical file systems, each of which is called a file system implementation ." </P> <P> The third layer is the physical file system . This layer is concerned with the physical operation of the storage device (e.g. disk). It processes physical blocks being read or written . It handles buffering and memory management and is responsible for the physical placement of blocks in specific locations on the storage medium . The physical file system interacts with the device drivers or with the channel to drive the storage device . </P>

Which data type supports only sequential access of objects