rk.4

UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.th RK IV 10/15/73
.sh NAME
rk  \*-  RK-11/RK03 (or RK05) disk
.sh DESCRIPTION
.it Rk?
refers to an entire RK03 disk as a single sequentially-addressed
file.
Its 256-word blocks are numbered 0 to 4871.
.s3
Drive numbers (minor devices)
of eight and larger are treated specially.
Drive 8+\fIx\fR is the \fIx\fR+1 way
interleaving of devices
rk0 to rk\fIx\fR.
Thus blocks on rk10 are distributed alternately
among rk0, rk1, and rk2.
.s3
The
.it rk
files
discussed above 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 RK files
begin with
.it rrk
and end with a number which selects the same disk
as the corresponding
.it rk
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/rk?, /dev/rrk?
.sh BUGS
Care should be taken in using the interleaved files.
First, the same drive should not be accessed simultaneously
using the ordinary name and as part of an interleaved file,
because the same physical
blocks
have in effect two different
names; this fools the system's buffering strategy.
Second, the combined files cannot be used for swapping
or raw I/O.