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1.1     ! root        1: .TH INTRO 4
        !             2: .SH NAME
        !             3: intro \- introduction to devices, line disciplines, and file systems
        !             4: .SH DESCRIPTION
        !             5: This section describes drivers for
        !             6: devices,
        !             7: stream line disciplines,
        !             8: and file systems.
        !             9: .PP
        !            10: Devices are accessed through
        !            11: special files of type
        !            12: .L S_IFBLK
        !            13: (block devices)
        !            14: or
        !            15: .L S_IFCHR
        !            16: (character devices);
        !            17: see
        !            18: .IR stat (2).
        !            19: Block devices use a block buffering scheme
        !            20: within the system,
        !            21: so that sectored devices like disks
        !            22: may be accessed a byte at a time.
        !            23: Character devices don't use the block buffers.
        !            24: Only block devices may be mounted as disk file systems.
        !            25: Most block devices
        !            26: have associated `raw' character devices
        !            27: that bypass all buffering for fast direct I/O.
        !            28: .PP
        !            29: The device associated with a special file is
        !            30: identified by a pair of numbers:
        !            31: a major device number
        !            32: naming the driver,
        !            33: and a minor device number
        !            34: picking some particular device or subunit.
        !            35: Major numbers are listed in
        !            36: .IR mknod (8).
        !            37: Minor numbers are specific to each driver;
        !            38: see the writeups in this section.
        !            39: Minor numbers are stored in a single unsigned byte;
        !            40: they are chosen from the range 0-255.
        !            41: .PP
        !            42: Some character devices are also
        !            43: stream devices.
        !            44: These use a different internal buffering mechanism
        !            45: to allow data to flow asynchronously.
        !            46: Various special operations are possible on streams;
        !            47: see
        !            48: .IR stream (4).
        !            49: .PP
        !            50: Line disciplines are
        !            51: processing modules that may be inserted into streams.
        !            52: They are identified by integers
        !            53: passed to the calls that insert and remove them.
        !            54: The C library
        !            55: contains global variables
        !            56: initialized to the numbers
        !            57: for various line disciplines;
        !            58: .IR stream (4)
        !            59: has a list.
        !            60: .PP
        !            61: There are several different types of file system:
        !            62: conventional disk volumes,
        !            63: remote file systems
        !            64: accessed
        !            65: by the system sending messages though a stream
        !            66: to a server as described in
        !            67: .IR netfs (8),
        !            68: a file system containing a file representing
        !            69: each process in the system,
        !            70: and so on.
        !            71: All of these
        !            72: appear the same to ordinary processes,
        !            73: except that not all file systems
        !            74: implement all operations;
        !            75: for example,
        !            76: a process file has a name,
        !            77: and may be opened, read, and written
        !            78: like an ordinary file,
        !            79: but may not be renamed because
        !            80: .IR proc (4)
        !            81: doesn't allow that.
        !            82: .PP
        !            83: File system types are
        !            84: identified by integers,
        !            85: used by and listed in
        !            86: .IR fmount (2).
        !            87: They are just magic numbers at present.
        !            88: .SH SEE ALSO
        !            89: .IR fmount (2),
        !            90: .IR stream (4),
        !            91: .IR mknod (8)

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