A special file is associated with a particular hardware device or other resource of the computer system. The operating system uses special files, sometimes called device files, to provide file I/O access to specific character and block device drivers.
Special files, at first glance, appear to be just like ordinary files, in that they:
However, there is an important difference between the two. An ordinary file is a logical grouping of data recorded on disk. A special file, on the other hand, corresponds to a device entity. Examples are:
Special files are distinguished from other files by having a file type (c or b, for character or block) stored in the i-nodes to indicate the type of device access provided. The i-node for the special file also contains the device major and minor numbers assigned to the device at device configuration time.
Several special files are provided with the operating system. By convention, special files are located in the /dev directory.
More information is provided about the following special files:
| 3270cn | Provides access to 3270 connection adapters by way of the 3270 connection adapter device driver. |
| bus | Provides access to the hardware bus by way of the machine I/O device driver. |
| cd | Provides access to the cdrom device driver. |
| console | Provides access to the system console. |
| dials | Provides access to the dials. |
| dump | Supports system dump. |
| entn | Provides access to the 3COM Ethernet adapters by way of the Ethernet device handler for this platform. |
| error | Supports error logging. |
| fd | Provides access to the diskette device driver. |
| fddin | Provides access to the FDDI device driver by way of the FDDI device handler. |
| GIO | Provides access to the graphics I/O (GIO) adapter. |
| ide | Provides access to the Integrated Device Electronics (IDE) adapter driver. |
| kbd | Provides access to the natively attached keyboard. |
| kmem and mem | Provides privileged read and write access to virtual memory. |
| lft | Implements a low-function terminal (LFT) device. |
| ide | Provides access to the IDE adapter device driver. |
| lp | Provides access to the line printer device driver. |
| lpfk | Provides access to the lighted program function key (LPFK) array. |
| lvdd | Provides access to the logical volume device driver. |
| mouse | Provides access to the natively attached mouse. |
| mpqi | Provides access to the Multiport Model 2 Adapter (MM2) SDLC device driver. |
| mpqn | Provides access to multiprotocol adapters by way of the Multiprotocol Quad Port (MPQP) device handler. |
| null | Provides access to the null device. |
| nvram | Provides access to platform-specific nonvolatile RAM used for system boot, configuration, and fatal error information. |
| omd | Provides access to the read/write optical device driver. |
| opn | Provides diagnostic interface to the Serial Optical Link device driver. |
| ops0 | Provides access to the Serial Optical Link device driver |
| pty | Provides the pseudo-terminal (pty) device driver. |
| random | Source of secure random output. |
| rcm | Provides application interface to obtain and relinquish status of a graphics process through the Rendering Context Manager (RCM) device driver. |
| rhdisk | Provides raw access to the physical volume (fixed-disk) device driver. |
| rmt | Provides access to the sequential-access bulk-storage medium device driver. |
| scsi | Provides access to the SCSI adapter device driver. |
| tablet | Provides access to the tablet. |
| tmscsi | Provides access to the SCSI Target-mode interface by way of the SCSI tmscsi device driver. |
| tokn | Provides access to the token-ring adapters by way of the token-ring device handler. |
| trace | Supports event tracing. |
| tty | Supports the controlling terminal interface. |
| urandom | Source of secure random output. |
| vty_server | Creates a tty-style connection from the partition on which a virtual terminal server is running to a virtual terminal (not a virtual terminal server) on another partition. |
| x25sn | Provides access to the X.25 Interface Co-Processor/2 adapters. |
File Formats Overview defines and describes file formats.
Header Files Overview describes header files.