A computer typically uses a wide range of peripheral and mass-storage devices. Your system, for example, probably has a SCSI disk drive, a keyboard and a mouse, and some kind of magnetic backup medium. Other commonly used devices include CD-ROM drives, printers and plotters, light pens, touch-sensitive screens, digitizers, and tablet-and-stylus pairs.
The Solaris software does not directly communicate with all these devices. Each type of device requires different data formats, protocols, and transmission rates.
A device driver is a low-level program that allows the operating system to communicate with a specific piece of hardware. The driver serves as the operating system's "interpreter" for that piece of hardware.