.th HP IV 2/9/75
.sh NAME
hp \*- RH-11/RP04 moving-head disk
.sh DESCRIPTION
The files
.it "hp0 ... hp7"
refer to sections of RP disk drive 0.
The files
.it "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.
.s3
The origin and size of the pseudo-disks on each drive are
as follows:
.s3
.br
	disk	start	length
.br
	0	0	9614
.br
	1	18392	65535
.br
	2	48018	65535
.br
	3	149644	20900
.br
	4	0	40600
.br
	5	41800	40600
.br
	6	83600	40600
.br
	7	125400	40600
.s3
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.
.s3
The
.it 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
.it rhp
and end with a number which selects the same disk
section as the corresponding
.it hp
file.
.s3
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
.it seek
calls should specify a multiple of 512 bytes.
.sh FILES
/dev/hp?, /dev/rhp?
.sh BUGS