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0 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)

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