RF(IV)                       10/15/73                      RF(IV)

     rf - RF11/RS11 fixed-head disk file

     This file refers to the concatenation of all RS-11 disks.

     Each  disk contains 1024 256-word blocks.  The length of the
     combined RF file is 1024X(minor+1) blocks.   That  is  minor
     device  zero  is  taken to be 1024 blocks long; minor device
     one is 2048, etc.

     The rf0 file accesses  the  disk  via  the  system's  normal
     buffering  mechanism and may be read and written without re-
     gard to physical disk records.  There is also a ``raw''  in-
     terface  which  provides for direct transmission between the
     disk and the user's read or write buffer.  A single read  or
     write  call  results in exactly one I/O operation and there-
     fore raw I/O is considerably more efficient when many  words
     are  transmitted.  The name of the raw RF file is rrf0.  The
     same minor device considerations hold for the raw  interface
     as for the normal interface.

     In  raw  I/O  the  buffer must begin on a word boundary, and
     counts should be a multiple of 512  bytes  (a  disk  block).
     Likewise  seek calls should specify a multiple of 512 bytes.

     /dev/rf0, /dev/rrf0

     The 512-byte restrictions on the raw device are  not  physi-
     cally necessary, but are still imposed.

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