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Command: hd | Section: 4 | Source: UNIX v7 | File: hd.4
HD(4) Kernel Interfaces Manual HD(4)
NAME
hd - ATA hard drive
DESCRIPTION
The octal representation of the minor device number is encoded dsp,
where d is the physical drive number, s indicates the disk slice (one
of the four ``fdisk partitions'' into which a PC hard disk may be di-
vided), and p selects a pseudodisk (subsection) within that drive and
slice. Disk slices are encoded as follows:
slice comment
0 whole disk
1 slice 1
2 slice 2
3 slice 3
4 slice 4
5 3rd UNIX slice
6 2nd UNIX slice
7 1st UNIX slice
Thus minor device number 0164 refers to pseudodisk 4 on the second UNIX
slice of physical drive 1.
For pseudodisks, the convention is suggested that 0 be used for the
root, 1 for swap, and 2 to refer to the whole disk, with others unre-
stricted.
The hd files access the disk via the system's normal buffering mecha-
nism 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 HD files begin with rhd. The same
minor device considerations hold for the raw interface as for the nor-
mal interface.
In raw I/O, counts should be a multiple of 512 bytes (a disk block).
Likewise lseek calls should specify a multiple of 512 bytes.
FILES
/dev/hd?, /dev/rhd?
BUGS
Pseudodisk definitions are hard-coded in the device driver source file.
HD(4)