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

     regard to physical disk records.  There is  also  a  ``raw''

     interface 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

     therefore 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

     physically necessary, but are still imposed.