HP 3000 Manuals

Accessing Files Programmer's Guide

Disk Files and Device Files 

The file system recognizes two basic types of files, classified on the
basis of the media on which they reside when processed:

   1.  Disk files, which are files residing on disk, are immediately
       accessible by the system and potentially shareable by several
       jobs/sessions at the same time. 

   2.  Device files are files currently being input to or output from any
       peripheral device except a disk.  When information exists on such
       a device but is not being processed, the file system cannot
       recognize it as a file.  Thus, information on a magnetic tape is
       not identified as a file until the tape is loaded onto a tape
       drive and reading begins; data being written to a line printer is
       no longer regarded as a file when output to the printer
       terminates. 
       A device file is considered nonshareable; it is accessed
       exclusively by the job or session that acquires it, and is owned
       by that job/session until the job/session explicitly releases it
       or terminates.


NOTE  Spooled device files, although temporarily residing on disk, are
      considered device files in the fullest sense because they are
      always originated on or destined for devices other than disk, and
      because you generally remain unaware of their storage on disk as an
      intermediate step in the spooling process.  Whether they deal with
      spooled or unspooled device files, your programs handle
      input/output as if the files reside on nonshareable devices.  The
      console operator, not the user, controls the spooling operation.

MPE/iX 5.0 Documentation