Interdata_v6/usr/doc/man/man4/dsk.4

Find at most related files.
including files from this version of Unix. 
.th DSK IV
.sh NAME
dsk - 10-megabyte disk
.sh DESCRIPTION
.it df?
and
.it dr?
refer to the fixed and removable platter respectively of a 10-megabyte
cartridge disk drive.
Each has 512-byte blocks numbered 0 to 9791.

The 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 bytes
are transmitted.
The names of the raw disk files are formed by prefixing
.it `r'
to the name of the corresponding disk.

In raw I/O the buffer must begin on a halfword boundary,
and counts should be a multiple of 512 bytes (a logical disk block).
Likewise seek calls should specify a multiple of 512 bytes.
.sh FILES
.ul 1
.nf
  Name    Device   Address
/dev/dr0   0/0       c6     removable disk (right-hand cabinet)
/dev/df0   0/1       c7     fixed disk             "
/dev/dr1   0/2       d6     removable disk (left-hand cabinet)
/dev/df1   0/3       d7     fixed disk             "

/dev/rdf?, /dev/rdr?         raw disks
.fi