RP(IV)                       2/21/74                       RP(IV)



NAME
     rp - RP-11/RP03 moving-head disk

DESCRIPTION
     The  files rp0 ... rp7 refer to sections of RP disk drive 0.
     The files rp8 ... rp15 refer to drive 1 etc.  This  is  done
     since the size of a full RP drive is 81200 blocks and inter-
     nally the system is only capable of addressing 65536 blocks.
     Also since the disk is so large, this allows it to be broken
     up into more manageable pieces.

     The origin and size of the pseudo-disks on each drive are as
     follows:

          disk start     length
          0    0    40600
          1    40600     40600
          2    0    9200
          3    72000     9200
          4    0    65535
          5    15600     65535
          6-7  unassigned

     It is unwise for all of these files to be present in one in-
     stallation, since there is overlap in addresses and  protec-
     tion  becomes a sticky matter.  Here is a suggestion for two
     useful configurations: If the root of the file system is  on
     some  other device and the RP used as a mounted device, then
     rp0 and rp1, which divide the disk into two equal size  por-
     tions,  is a good idea.  Other things being equal, it is ad-
     vantageous to have two equal-sized portions  since  one  can
     always  be copied onto the other, which is occasionally use-
     ful.

     If the RP is the only disk and has to contain the  root  and
     the  swap  area,  the root can be put on rp2 and a mountable
     file system on rp5.  Then the swap space can be put  in  the
     unused  blocks 9200 to 15600 of rp0 (or, equivalently, rp4).
     This arrangement puts the root file system, the  swap  area,
     and  the  i-list  of the mounted file system relatively near
     each other and thus tends to minimize head movement.

     The rp files access the disk via the system's normal buffer-
     ing  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 RP files begin with rrp
     and end with a number which selects the same disk section as
     the corresponding rp 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).


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RP(IV)                       2/21/74                       RP(IV)


     Likewise  seek calls should specify a multiple of 512 bytes.

FILES
     /dev/rp?, /dev/rrp?

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