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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 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 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.
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