software that controls one specific type of device
software must match hardware
usually for a particular model of some type of device
or a class of similar devices
e.g., disks compatible with IBM 3380
e.g., dumb terminal
trends:
more and more of device driver is in tabular format
low--level device drivers can be easily added and removed from the system
interfaces to devices are becoming simpler as devices become more autononous
(e.g., recent disk devices manage their own sectors, tracks, and cylinders)