HP(IV)                       2/9/75                        HP(IV)


     hp - RH-11/RP04 moving-head disk


     The files hp0 ... hp7 refer to sections of RP disk drive  0.

     The  files  hp8 ... hp15 refer to drive 1 etc.  This is done

     since the size of a full RP  drive  is  170,544  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       9614

             1       18392   65535

             2       48018   65535

             3       149644  20900

             4       0       40600

             5       41800   40600

             6       83600   40600

             7       125400  40600

     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.

     The hp  files  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 rhp and end with a number which selects the  same  disk

     section as the corresponding hp 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/hp?, /dev/rhp?