Transforming I/O Request to Hardware

Transforming I/O Requests to Hardware Operations

* Users appeal data using file names, which must ultimately be mapped to specific blocks of data from a specific device managed by a specific device driver.

* DOS uses the colon separator to specify a particular device ( e.g. C:, LPT:, etc. )

* UNIX uses a mount table to map filename append ( e.g. /usr ) to specific mounted devices. Where many entries in the mount table match different appends of the filename the one that matches the longest append is chosen. ( e.g. /usr/home instead of /usr where both subsits in the mount table and both match the required file. )

* UNIX uses special device files, usually located in /dev, to represent and process physical devices directly.

• Each device file has a major and minor number related with it, stored and

displayed where the file size could normally go.

• The high number is an index into a table of device drivers, and implies which

device driver handles this device. ( E.g. the disk drive handler. )

• The minor number is a parameter moved to the device driver, and implies which

particular device is to be processed, out of the many which may be handled by a

particular device driver. ( e.g. a specific disk drive or partition. )

* A series of lookup tables and mappings makes the access of different devices adaptable, and somewhat transparent to users.

* Figure explains the steps taken to process a ( blocking ) read request: