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The first experience was in DOS. 
Here the difference between a TSR (terminate-and-stay-resident)
and a device driver can be very small. Of course the device
driver begins with a very special header, while a TSR is
actually an executable that keeps some of its code active while
the system remains on.
Now it can be in the MS Windows 
device driver model. There have been various flavours,
commencing with the very powerful VXD and SYS file of Window 3.1
and 3.11, through Windows 95/98 SE, and Windows NT, onto the current
Microsoft Windows 2000, XP (WDM), Operating Systems, and seemingly ever onwards.
Nearly always in my case the emphasis has been computer to
computer 
communications.
In the early programming days that was PEP (aka Personal
Emulation Package). This special "driver" took over
just about all DOS functions and allowed toggle between the
"captured" DOS OS and the PEP Uniscope character
emulation screen.
Originally communication was via a purpose built AT Bus card 
that performed synchronous data communications up to the fastest
speed at that time of 9,600 baud. A PEP card, so the real
"device driver" part of the code provided the bridge
between the on board Zilog 8530 sync. chip and the
"screen". More can be read about the Company I ran to
sell this PEP product in my Working Experience, Page 1,
and Page 2.