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Unix Version 7 - man page for hp (v7 section 4)

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HP(4)											    HP(4)

       hp - RH-11/RP04, RP05, RP06 moving-head disk

       The  octal  representation of the minor device number is encoded idp, where i is an inter-
       leave flag, d is a physical drive number, and p is a  pseudodrive  (subsection)	within	a
       physical unit.  If i is 0, the origins and sizes of the pseudodisks on each drive, counted
       in cylinders of 418 512-byte blocks, are:

	    disk start	   length
	    0	 0    23
	    1	 23   21
	    2	 0    0
	    3	 0    0
	    4	 44   386
	    5	 430  385
	    6	 44   367
	    7	 44   771

       If i is 1, the minor device consists of the specified  pseudodisk  on  drives  numbered	0
       through	the designated drive number.  Successively numbered blocks are distributed across
       the drives in rotation.

       Systems distributed for these devices use disk 0 for the root, disk 1  for  swapping,  and
       disk 4 (RP04/5) or disk 7 (RP06) for a mounted user file system.

       The  block  files  access  the disk via the system's normal buffering mechanism and may be
       read and written without regard to physical disk records.

       A `raw' interface 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 there-
       fore raw I/O is considerably more efficient when many words are transmitted.  The names of
       the raw files conventionally begin with an extra `r.'  In raw I/O the buffer must begin on
       a word boundary, and raw I/O to an interleaved device  is  likely  to  have  disappointing

       /dev/rp?, /dev/rrp?


       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.

       Raw device drivers don't work on interleaved devices.

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