The OS supports four unique File Management Subsystems at the time of this writing. Version 1A is the original version. Version 1B is a slightly modified version of 1A and is the one described in this document. Most of this discussion applies as well to Version 2, that handles a double-density diskette (720 256-byte sectors) in addition to the single-density diskette (720 128-byte sectors). Version 3 has all new file/directory/map structures and can possibly contain changes to your interface as well.
The File Management Subsystem includes a disk-bootable (RAM-resident) Disk File Manager (DFM) that maintains a collection of named files on diskettes. Up to 4 disk drives (D1: through D4:) can be accessed and up to 64 files per diskette can be accessed. The system diskettes supplied by ATARI allow a single disk drive (D1) and up to 3 OPEN files, but you can alter these numbers as described later in this section.
The Disk File Manager supports the following CIO Functions:
OPEN FILE OPEN DIRECTORY CLOSE GET CHARACTERS GET RECORD PUT CHARACTERS PUT RECORD GET STATUS NOTE POINT LOCK UNLOCK DELETE RENAME FORMAT
