.th RP IV 2/21/74
.sh NAME
rp \*- RP-11/RP03 moving-head disk
.sh DESCRIPTION
The files
.it "rp0 ... rp7"
refer to sections of RP disk drive 0.
The files
.it "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.
.s3
The origin and size of the pseudo-disks on each drive are
as follows:
.s3
.br
	disk	start	length
.br
	0	0	40600
.br
	1	40600	40600
.br
	2	0	9200
.br
	3	72000	9200
.br
	4	0	65535
.br
	5	15600	65535
.br
	6-7	unassigned
.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.
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
.it rp0
and
.it 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.
.s3
If the RP is the only disk and has to
contain the root and the swap area,
the root can be put on
.it rp2
and a mountable file system on
.it rp5.
Then the swap space can be put in the
unused blocks 9200 to 15600 of
.it rp0
(or, equivalently,
.it 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.
.s3
The
.it rp
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 rrp
and end with a number which selects the same disk
section as the corresponding
.it rp
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/rp?, /dev/rrp?
.sh BUGS