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


     rp - RP-11/RP03 moving-head disk


     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

     internally  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


             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

     installation,  since  there  is  overlap  in  addresses  and

     protection 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 portions, is a good  idea.   Other  things  being

     equal,  it  is advantageous to have two equal-sized portions

     since one can always be copied  onto  the  other,  which  is

     occasionally useful.

     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 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 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).

     Likewise seek calls should specify a multiple of 512 bytes.


     /dev/rp?, /dev/rrp?