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E.2.5.  /proc/devices

This file displays the various character and block devices currently configured (not including devices whose modules are not loaded). Below is a sample output from this file:
Character devices:
  1 mem
  4 /dev/vc/0
  4 tty
  4 ttyS
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
  10 misc
  13 input
  29 fb
  36 netlink
  128 ptm
  136 pts
  180 usb

Block devices:
  1 ramdisk
  3 ide0
  9 md
  22 ide1
  253 device-mapper
  254 mdp
The output from /proc/devices includes the major number and name of the device, and is broken into two major sections: Character devices and Block devices.
Character devices are similar to block devices, except for two basic differences:
  1. Character devices do not require buffering. Block devices have a buffer available, allowing them to order requests before addressing them. This is important for devices designed to store information — such as hard drives — because the ability to order the information before writing it to the device allows it to be placed in a more efficient order.
  2. Character devices send data with no preconfigured size. Block devices can send and receive information in blocks of a size configured per device.
For more information about devices refer to the following installed documentation:
/usr/share/doc/kernel-doc-<kernel_version>/Documentation/devices.txt