RK(4) Kernel Interfaces Manual RK(4)
rk - RK-11/RK03 or RK05 disk
Rk? refers to an entire disk as a single sequentially-addressed file.
Its 256-word blocks are numbered 0 to 4871. Minor device numbers are
drive numbers on one controller.
The rk files discussed above access the disk via the system's normal
buffering mechanism and may be read and written without regard to phys-
ical disk records. There is also a `raw' interface which provides for
direct transmission between the disk and the user's read or write buf-
fer. 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 rrk and end
with a number which selects the same disk as the corresponding rk file.
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 seek calls should
specify a multiple of 512 bytes.
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.