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RK(4)                      Kernel Interfaces Manual                      RK(4)

       rk  -  RK-11/RK03 or RK05 disk

       Rk?   refers to an entire disk as a single sequentially-addressed file.
       Its 256-word blocks are numbered 0 to 4871.  Minor device  numbers  are
       drive numbers on one controller.

       The  rk  files  discussed above access the disk via the system's normal
       buffering mechanism and may be read and written without regard to phys-
       ical  disk records.  There is also a `raw' interface which provides for
       direct transmission between the disk and the user's read or write  buf-
       fer.   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?

       In raw I/O read and write(2) truncate file offsets  to  512-byte  block
       boundaries,  and  write  scribbles  on  the  tail of incomplete blocks.
       Thus, in programs that are likely to access raw  devices,  read,  write
       and lseek(2) should always deal in 512-byte multiples.