Devices as Special Files

Devices are treated as files. They are represented in the file system by special files. In the Solaris operating environment these files reside in the /devices directory hierarchy.

Special files can be of type block or character. The type indicates which kind of device driver operates the device. Drivers can be implemented to operate on both types. For example, disk drivers export a character interface for use by the fsck(1) and mkfs(1) utilities, and a block interface for use by the file system.

Associated with each special file is a device number (dev_t). This consists of a major number and a minor number. The major number identifies the device driver associated with the special file. The minor number is created and used by the device driver to further identify the special file. Usually, the minor number is an encoding that identifies the device instance the driver should access and the type of access to perform. The minor number, for example, could identify a tape device used for backup and also specify whether the tape needs to be rewound when the backup operation is complete.