V7M/man/man4/rf.4

.TH RF 4 
.SH NAME
rf \- RF11/RS11 fixed-head disk file
.SH DESCRIPTION
This file refers to the
concatenation of all RS-11 disks.
.PP
Each disk contains 1024 256-word blocks.
The length of the combined RF file is
1024\(mu(minor+1) blocks.
That is minor device zero
is taken to be
1024 blocks long;
minor device one is 2048,
etc.
.PP
The
.I rf0
file
accesses 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 name of the raw RF file is
.IR rrf0 .
The same minor device considerations
hold for the raw interface as for the normal interface.
.PP
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
.I seek
calls should specify a multiple of 512 bytes.
.SH FILES
/dev/rf0, /dev/rrf0
.SH BUGS
The 512-byte restrictions on the raw device are not
physically necessary,
but are still imposed.