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

     treated specially.  Drive 8+x is the x+1 way interleaving of

     devices rk0 to rkx.  Thus blocks  on  rk10  are  distributed

     alternately among rk0, rk1, and rk2.

     The rk  files  discussed  above  access  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 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,

     because   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.