Fuel Pumps in diesel engines are considered "the heart" and for how crucial they are they are surprizingly reliable.  Compared to a gasoline engine, a diesel engine fuel pump does the work of the carburettor / injectors, distributor and ignition setup including spark plugs, and fuel pump in one simple unit.

Because diesel engines run more effecently than gas motors in most situations, the need to make diesel engines electronic has been minimal.  For example Cummins engines in Dodge trucks remained almost 100% mechanical operation until 1999, versus computerized fuel injection in gasoline engines which became popular in the late 70s and 80s.  The fuel pump is mechanically driven from a gear or tiing belt.  Most are setup in either a rotary function or an inline function.  For example Bosch fuel pumps found in Cummins engines are available in both forms.  They take in fuel, control how and how much should be released, and at what time.  They are sort of like precision gear driven machines, like a mechanical watch.

All about lubrication of fuel pumps
About Bosch Fuel Pumps
NEVER adjust the timing on a diesel fuel pump
About Electronic Diesel Injection Control (EDIC)