RK(IV)                       10/15/73                      RK(IV)

     rk  -  RK-11/RK03 (or RK05) disk

     Rk?  refers to an entire RK03 disk as a single sequentially-
     addressed file.  Its 256-word blocks are numbered 0 to 4871.

     Drive numbers (minor devices) of eight and larger are treat-
     ed specially.  Drive 8+x is the x+1 way interleaving of  de-
     vices  rk0  to rkx.  Thus blocks on rk10 are distributed al-
     ternately among rk0, rk1, and rk2.

     The rk files discussed above access the disk  via  the  sys-
     tem'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 be-
     tween the disk and the user's read or write buffer.  A  sin-
     gle  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 names of the raw RK files
     begin with rrk and end with a number which selects the  same
     disk as the corresponding rk file.

     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/rk?, /dev/rrk?

     Care should be taken in using the interleaved files.  First,
     the  same  drive should not be accessed simultaneously using
     the ordinary name and as part of an  interleaved  file,  be-
     cause  the same physical blocks have in effect two different
     names; this fools the system's buffering strategy.   Second,
     the combined files cannot be used for swapping or raw I/O.

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